diff --git a/docs/content/docs/features/custom-schemas/container-blocks.mdx b/docs/content/docs/features/custom-schemas/container-blocks.mdx
new file mode 100644
index 0000000000..9ad7e4916d
--- /dev/null
+++ b/docs/content/docs/features/custom-schemas/container-blocks.mdx
@@ -0,0 +1,280 @@
+---
+title: Container Blocks
+description: Learn how to create custom blocks that hold other blocks as their body
+---
+
+# Container Blocks
+
+A *container block* is a custom block that holds other blocks as its body — like a Notion-style callout wrapping a paragraph and a code block, a toggle with a title and a body, or a multi-column layout. BlockNote's built-in multi-column blocks (`columnList` / `column`) are implemented with this same mechanism.
+
+Take a look at the demo below, in which we add a custom callout block that can contain any other blocks:
+
+<Example name="custom-schema/container-block" />
+
+## Declaring a Container Block
+
+Add the `children` option to your block config (created with [`createBlockSpec` or `createReactBlockSpec`](/docs/features/custom-schemas/custom-blocks)). Everything about it is optional, so the smallest container is:
+
+```typescript
+const createCallout = createReactBlockSpec(
+  {
+    type: "callout",
+    propSchema: {},
+    content: "none",
+    // Makes this a container: its body is other blocks.
+    children: {},
+  },
+  {
+    // Child blocks mount into the element you attach `contentRef` to.
+    render: (props) => <div className="callout" ref={props.contentRef} />,
+  },
+);
+```
+
+`children: {}` accepts any block, requires at least one, and can never throw: when a container is created without children, BlockNote fills it with whatever its schema requires.
+
+At runtime the contained blocks live on `block.children` — the same field used for indented (nested) blocks:
+
+```json
+{
+  "id": "callout-1",
+  "type": "callout",
+  "props": {},
+  "children": [
+    {
+      "id": "para-1",
+      "type": "paragraph",
+      "content": [{ "type": "text", "text": "Hello", "styles": {} }],
+      "children": []
+    }
+  ]
+}
+```
+
+### Where children render
+
+There is only one placement mechanism, and it is the one you already use for inline content. `contentRef` (React) / `contentDOM` (vanilla) marks **the block's editable region**; what goes in that region depends on the block:
+
+| block | `contentRef` element holds |
+| --- | --- |
+| `content: "inline"`, no `children` | its inline content |
+| `content: "none"` + `children` | its child blocks |
+| `content: "inline"` + `children` | its inline content, then its child blocks |
+
+A `content: "none"` block *without* `children` is the only kind with nothing to place, and it's the only kind that isn't offered a `contentRef` at all.
+
+Container blocks own their entire outer DOM — BlockNote doesn't wrap them in the usual block element. Whatever element your `render` returns *is* the block's element, and BlockNote stamps the attributes it relies on for parsing and UI positioning onto it: `data-node-type`, `data-id`, and each non-default prop as a `data-*` attribute. You write a plain `<div className="callout">` and `data-flavor="info"` lands on it, in the live editor and in serialized HTML alike.
+
+<Callout type="info">
+  _Because the framework wrappers React puts above your element carry `display:
+  contents`, they contribute no box: your element lays out exactly as if it were
+  the block's root. Selection is mirrored onto it as a `data-selected`
+  attribute, so `[data-selected]` is what you style for the selected state._
+</Callout>
+
+## Containers with their own content
+
+A container can have inline content *of its own* as well as children — a toggle's title with its body beneath it, a card header, a callout whose first line is real rich text rather than a plain `<input>`. Combine `content: "inline"` with `children`, and place both with the same single `contentRef`:
+
+```typescript
+const createToggle = createReactBlockSpec(
+  {
+    type: "toggle",
+    propSchema: {},
+    // The toggle's own title...
+    content: "inline",
+    // ...and its body.
+    children: { min: 0 },
+  },
+  {
+    render: (props) => (
+      <div className="toggle">
+        <span className="chevron" contentEditable={false} />
+        <div className="toggle-main" ref={props.contentRef} />
+      </div>
+    ),
+  },
+);
+```
+
+This is purely additive: adding `children` to an existing block is one config line and **zero render changes**. The block keeps its `Block` JSON shape — `content` for its own content, `children` for its body — identical to any other nested block.
+
+### The two regions
+
+Inside the `contentRef` element, BlockNote renders two sibling elements with stable attributes derived from the block type:
+
+- `[data-content-type="<type>"]` — the block's own inline content.
+- `[data-children-of="<type>"]` — its child blocks.
+
+You never place these yourself; you style them. The host element between them carries `display: contents`, so a grid on your own root reaches them directly:
+
+```css
+.toggle      { display: grid; grid-template-columns: auto 1fr; }
+.toggle-main { display: contents; }
+.chevron                     { grid-column: 1; grid-row: 1; }
+[data-content-type="toggle"] { grid-column: 2; grid-row: 1; }
+[data-children-of="toggle"]  { grid-column: 2; grid-row: 2; }
+```
+
+<Callout type="warn">
+  **Two limits, both imposed by ProseMirror:** reading order is always
+  content-then-children, and your own markup cannot be interleaved between the
+  two regions or wrap only one of them. A grid (or `order`) can reorder them
+  *visually*; the DOM order is fixed.
+</Callout>
+
+## `children` options
+
+| Option | Default | Description |
+| --- | --- | --- |
+| `allow` | any block | What may appear as a child. See [Restricting children](#restricting-children). |
+| `min` / `max` | `1` / unbounded | How many children are allowed. Compiled into the editor schema. |
+| `sequence` | — | An *ordered* body instead of a uniform one. Mutually exclusive with `allow`/`min`/`max`. See [Ordered children](#ordered-children). |
+| `default` | — | Partial blocks to create the container with when it's inserted without an explicit `children` array. Validated against the rest of the config when the schema is created. Omit it and BlockNote fills the container with whatever its schema requires. |
+| `unwrapWhenEmptied` | `false` | As children are emptied out, drop the emptied ones and — once fewer non-empty children remain than `min` — replace the container with its survivors, or remove it entirely when none are left. Column lists use this so emptied columns disappear and a one-column list unwraps. |
+| `exitOnEnter` | `true` | Pressing Enter on an empty block that is the last child moves that block out of the container, list-style. Disable it to keep the cursor inside (columns do this). |
+
+`placement` sits next to `children` on the block config rather than inside it, because it's a fact about *this* block rather than about its children:
+
+| Option | Default | Description |
+| --- | --- | --- |
+| `placement` | `"anywhere"` | `"containerOnly"` restricts the block to containers that name it in `children.allow.containers` — like a `column`, which only makes sense inside a `columnList`. Only valid on container blocks. |
+
+Purely behavioral options that apply to *every* block kind stay in the block implementation's `meta`:
+
+| Meta option | Default | Description |
+| --- | --- | --- |
+| `draggable` | `true` | Whether the block gets a side menu drag handle. A block that opts out is skipped when looking for a handle, so the handle falls through to the nearest draggable ancestor. |
+
+<Callout type="warn">
+  _`unwrapWhenEmptied` never destroys typed text: for a container with its own
+  content, it does nothing at all while that content is non-empty. And without
+  it, a container that drops below `min` isn't unwrapped — ProseMirror refills
+  it with an empty child instead._
+</Callout>
+
+## Restricting children
+
+`allow` has two fields, because the document schema can make exactly two distinctions:
+
+```typescript
+allow?: {
+  // Whether regular (non-container) blocks are allowed.
+  blocks?: boolean;
+  // Which container-block types are allowed: `true`, `false`, or a list.
+  containers?: boolean | string[];
+}
+```
+
+Container blocks are their own ProseMirror node type, so naming them is exact. Every **regular** block — paragraph, heading, code block — is the *same* ProseMirror node internally, so "only headings" is not something the schema can enforce. Rather than offer an option that silently does nothing, `allow.blocks` is a boolean. Naming a regular block type in `allow.containers` is a hard error that says so.
+
+This is exactly how the multi-column blocks are defined:
+
+```typescript
+// The outer container: only columns, at least two of them.
+children: {
+  allow: { blocks: false, containers: ["column"] },
+  min: 2,
+  unwrapWhenEmptied: true,
+  exitOnEnter: false,
+}
+
+// The column: holds any blocks, but only lives inside a columnList.
+children: { exitOnEnter: false },
+placement: "containerOnly",
+```
+
+## Ordered children
+
+`sequence` replaces `allow`/`min`/`max` with a list of *positions*. Each slot holds exactly one child unless it declares a `count`:
+
+```typescript
+children: {
+  sequence: [
+    { allow: { blocks: false, containers: ["cardHeader"] } },
+    { allow: { blocks: false, containers: ["cardBody"] } },
+  ],
+}
+```
+
+That compiles to the ProseMirror content expression `cardHeader cardBody`, so the order is enforced by the document model itself: a card built as `[body, header]` is rejected before it can reach the document, and a card inserted with no children auto-fills one of each.
+
+`count` takes a number for an exact count, or `{ min, max }`:
+
+```typescript
+children: {
+  sequence: [
+    // Exactly one header.
+    { allow: { blocks: false, containers: ["cardHeader"] } },
+    // Then one or more blocks.
+    { count: { min: 1 } },
+  ],
+}
+```
+
+The uniform form is exactly sugar for a one-slot sequence: `{ allow, min, max }` is `{ sequence: [{ allow, count: { min, max } }] }`.
+
+## Inserting into a container
+
+`editor.insertBlocks` takes two nested placements alongside the sibling ones:
+
+```typescript
+// Siblings of the reference block:
+editor.insertBlocks([{ type: "paragraph" }], calloutId, "before");
+editor.insertBlocks([{ type: "paragraph" }], calloutId, "after");
+
+// Nested inside it, as its first or last child:
+editor.insertBlocks([{ type: "paragraph" }], calloutId, "start");
+editor.insertBlocks([{ type: "paragraph" }], calloutId, "end");
+```
+
+The nested placements are what addresses a container with no children to point at — a `min: 0` container that is currently empty has no child block to insert before or after. Whether a block fits is answered by the schema, so it's your `children` config that decides.
+
+## Validation
+
+Configurations are checked when the schema is created, and fail up front with a message naming the block. Beyond unknown block types and impossible `default` children, this catches:
+
+- an `allow` that permits nothing, or `allow.containers` naming a regular block type;
+- an empty `sequence`, and `content: "table"` combined with `children`;
+- a `placement: "containerOnly"` block that no container accepts, or `placement` on a non-container;
+- **container cycles** — a container that (transitively) requires a child that requires it back could never be created. Slots that allow regular blocks break the cycle, since they're always satisfiable.
+
+## Parsing HTML into a container
+
+Containers go through the same parsing path as regular blocks. The default rule matches the marker BlockNote puts on the block's root, `[data-node-type="<type>"]`, which is what makes HTML produced by BlockNote round-trip.
+
+To recognize *foreign* HTML, add `implementation.parse` — it returns the block's props, or `undefined` to decline:
+
+```typescript
+{
+  render: (props) => <div className="card" ref={props.contentRef} />,
+  parse: (el) =>
+    el.classList.contains("card")
+      ? { tone: el.getAttribute("data-tone") ?? undefined }
+      : undefined,
+}
+```
+
+With no `parseContent`, ProseMirror parses the element's children with the normal block rules, so `<div class="card"><p>…</p><h1>…</h1></div>` becomes a card with a paragraph and a heading. Supply `parseContent` only if you need to build the body yourself; inline nodes it returns become paragraph children, except a leading inline run in a container that has its own content, which becomes that content.
+
+`runsBefore` orders your parse rule against other blocks'. On a container it may only name **other containers**: container nodes register in a priority band below regular blocks, so a container can never be ordered ahead of one — a container's `tag: "*"` rule is always considered after every regular block's. Naming a regular block there is an error rather than a silent no-op.
+
+<Callout type="warn">
+  **`allow` does not filter what a user pastes.** Pasted HTML is parsed with
+  `blockGroup` as its top node, and ProseMirror's fitting algorithm places
+  content your container's expression rejects *after* the container rather than
+  dropping it. `allow` constrains the document model, not the parser.
+</Callout>
+
+## Interop behavior
+
+- **HTML**: containers serialize to a `<div data-node-type="...">` with their children nested inside and non-default props as `data-*` attributes, and parse back losslessly. A container with its own content serializes its two regions as `[data-content-type]` and `[data-children-of]` elements.
+- **External HTML** (`blocksToHTMLLossy`, copy to another app) is intentionally semantic and lossy. Override `toExternalHTML` and return a `childrenDOM` to say where children belong in your own markup — this is how toggles export as `<details>`.
+- **Markdown**: containers are flattened — their children are exported in order, and Markdown import never produces containers.
+- **Exporters** (`@blocknote/xl-docx-exporter`, `xl-pdf-exporter`, `xl-odt-exporter`, `xl-email-exporter`): container blocks require an explicit block mapping that places their children; a missing mapping throws a clear error.
+
+## Editable fields that aren't document content
+
+Not every editable field belongs in the document. If a field doesn't need rich text formatting, comments, or multiplayer cursors — a name, a URL, a label — store it as a **string prop** and render a regular `<input>` inside the block, in a `contentEditable={false}` wrapper, committing the value with `editor.updateBlock`. The callout demo at the top of this page does exactly that for its title.
+
+Reach for a container's own `content: "inline"` when the field *is* prose, and for a string prop when it's data.
diff --git a/docs/content/docs/features/custom-schemas/custom-blocks.mdx b/docs/content/docs/features/custom-schemas/custom-blocks.mdx
index ff25cf838c..7f919322f4 100644
--- a/docs/content/docs/features/custom-schemas/custom-blocks.mdx
+++ b/docs/content/docs/features/custom-schemas/custom-blocks.mdx
@@ -72,6 +72,12 @@ type BlockConfig = {
   alert, so we set `content` to `"inline"`._
 </Callout>
 
+<Callout type="info">
+  _Any block can also hold **other blocks** as its body by declaring the
+  `children` option — with or without inline content of its own. See [Container
+  Blocks](/docs/features/custom-schemas/container-blocks)._
+</Callout>
+
 `propSchema:` The `PropSchema` specifies the props that the block supports. Block props (properties) are data stored with your Block in the document, and can be used to customize its appearance or behavior.
 
 ```typescript
diff --git a/examples/06-custom-schema/09-container-block/.bnexample.json b/examples/06-custom-schema/09-container-block/.bnexample.json
new file mode 100644
index 0000000000..3de7330631
--- /dev/null
+++ b/examples/06-custom-schema/09-container-block/.bnexample.json
@@ -0,0 +1,15 @@
+{
+  "playground": true,
+  "docs": true,
+  "author": "nickthesick",
+  "tags": [
+    "Intermediate",
+    "Blocks",
+    "Custom Schemas",
+    "Suggestion Menus",
+    "Slash Menu"
+  ],
+  "dependencies": {
+    "react-icons": "^5.5.0"
+  }
+}
diff --git a/examples/06-custom-schema/09-container-block/README.md b/examples/06-custom-schema/09-container-block/README.md
new file mode 100644
index 0000000000..9e4ee82060
--- /dev/null
+++ b/examples/06-custom-schema/09-container-block/README.md
@@ -0,0 +1,22 @@
+# Container Block
+
+In this example, we create a custom `Callout` block that holds **other blocks** as its body — like a Notion-style callout that can wrap a paragraph followed by a code block, or any combination of nested blocks.
+
+The block declares the `children` config on `BlockConfig`. `children: { min: 1, default: [{ type: "paragraph" }] }` makes it a container: its child blocks mount into the element the render passes `contentRef` to, and live on `block.children` at runtime.
+
+The callout's **title** demonstrates the complementary "string prop slot" pattern: a field that doesn't need rich text, comments, or multiplayer cursors can live in a plain string prop, edited through a regular `<input>` rendered inside the block (in a `contentEditable={false}` wrapper) and committed via `editor.updateBlock`. A field that _is_ prose belongs in the block's own `content: "inline"` instead.
+
+We also wire up a Slash Menu item to insert the callout, and render the document JSON next to the editor so you can inspect the structure of the nested blocks.
+
+**Try it out:**
+
+- Press the "/" key inside the callout's body and add a code block, heading, or list — anything goes.
+- Type a title into the title field — it's stored on `block.props.title`, not as document content.
+- Watch the JSON panel on the right update as you edit; the callout's children appear in `block.children`.
+- Insert a new callout via the Slash Menu (search "callout").
+
+**Relevant Docs:**
+
+- [Container Blocks](/docs/features/custom-schemas/container-blocks)
+- [Custom Blocks](/docs/features/custom-schemas/custom-blocks)
+- [Editor Setup](/docs/getting-started/editor-setup)
diff --git a/examples/06-custom-schema/09-container-block/index.html b/examples/06-custom-schema/09-container-block/index.html
new file mode 100644
index 0000000000..19321f77b5
--- /dev/null
+++ b/examples/06-custom-schema/09-container-block/index.html
@@ -0,0 +1,14 @@
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Container Block</title>
+    <script>
+      <!-- AUTO-GENERATED FILE, DO NOT EDIT DIRECTLY -->
+    </script>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="./main.tsx"></script>
+  </body>
+</html>
diff --git a/examples/06-custom-schema/09-container-block/main.tsx b/examples/06-custom-schema/09-container-block/main.tsx
new file mode 100644
index 0000000000..1260513388
--- /dev/null
+++ b/examples/06-custom-schema/09-container-block/main.tsx
@@ -0,0 +1,11 @@
+// AUTO-GENERATED FILE, DO NOT EDIT DIRECTLY
+import React from "react";
+import { createRoot } from "react-dom/client";
+import App from "./src/App.jsx";
+
+const root = createRoot(document.getElementById("root")!);
+root.render(
+  <React.StrictMode>
+    <App />
+  </React.StrictMode>,
+);
diff --git a/examples/06-custom-schema/09-container-block/package.json b/examples/06-custom-schema/09-container-block/package.json
new file mode 100644
index 0000000000..d92c915975
--- /dev/null
+++ b/examples/06-custom-schema/09-container-block/package.json
@@ -0,0 +1,31 @@
+{
+  "name": "@blocknote/example-custom-schema-container-block",
+  "description": "AUTO-GENERATED FILE, DO NOT EDIT DIRECTLY",
+  "type": "module",
+  "private": true,
+  "version": "0.12.4",
+  "scripts": {
+    "start": "vp dev",
+    "dev": "vp dev",
+    "build:prod": "tsc && vp build",
+    "preview": "vp preview"
+  },
+  "dependencies": {
+    "@blocknote/ariakit": "latest",
+    "@blocknote/core": "latest",
+    "@blocknote/mantine": "latest",
+    "@blocknote/react": "latest",
+    "@blocknote/shadcn": "latest",
+    "@mantine/core": "^9.0.2",
+    "@mantine/hooks": "^9.0.2",
+    "react": "^19.2.3",
+    "react-dom": "^19.2.3",
+    "react-icons": "^5.5.0"
+  },
+  "devDependencies": {
+    "@types/react": "^19.2.3",
+    "@types/react-dom": "^19.2.3",
+    "@vitejs/plugin-react": "^6.0.1",
+    "vite-plus": "^0.1.24"
+  }
+}
diff --git a/examples/06-custom-schema/09-container-block/src/App.tsx b/examples/06-custom-schema/09-container-block/src/App.tsx
new file mode 100644
index 0000000000..8945f4a31a
--- /dev/null
+++ b/examples/06-custom-schema/09-container-block/src/App.tsx
@@ -0,0 +1,118 @@
+import { BlockNoteSchema, defaultBlockSpecs } from "@blocknote/core";
+import {
+  filterSuggestionItems,
+  insertOrUpdateBlockForSlashMenu,
+} from "@blocknote/core/extensions";
+import "@blocknote/core/fonts/inter.css";
+import { BlockNoteView } from "@blocknote/mantine";
+import "@blocknote/mantine/style.css";
+import {
+  SuggestionMenuController,
+  getDefaultReactSlashMenuItems,
+  useCreateBlockNote,
+} from "@blocknote/react";
+import { useEffect, useState } from "react";
+import { RiChatQuoteLine } from "react-icons/ri";
+
+import { createCallout } from "./Callout";
+import "./styles.css";
+
+// Schema with the default blocks plus our custom Callout container block.
+const schema = BlockNoteSchema.create().extend({
+  blockSpecs: {
+    ...defaultBlockSpecs,
+    callout: createCallout(),
+  },
+});
+
+// Slash menu item to insert a Callout. Because Callout is a container block,
+// inserting one with no children causes BlockNote to seed it with the block's
+// configured `children.default` (a single paragraph here).
+const insertCallout = (editor: typeof schema.BlockNoteEditor) => ({
+  title: "Callout",
+  subtext: "Container block that wraps other blocks",
+  onItemClick: () =>
+    insertOrUpdateBlockForSlashMenu(editor, {
+      type: "callout",
+    }),
+  aliases: ["callout", "container", "alert", "note", "tip", "info"],
+  group: "Basic blocks",
+  icon: <RiChatQuoteLine />,
+});
+
+type AppBlock = (typeof schema.BlockNoteEditor)["document"][number];
+
+export default function App() {
+  const [blocks, setBlocks] = useState<AppBlock[]>([]);
+
+  const editor = useCreateBlockNote({
+    schema,
+    initialContent: [
+      {
+        type: "paragraph",
+        content: "Welcome — this demo shows the new container block kind.",
+      },
+      {
+        type: "callout",
+        props: { flavor: "tip" },
+        children: [
+          {
+            type: "paragraph",
+            content: "Callouts can hold any block as their body.",
+          },
+          {
+            type: "paragraph",
+            content:
+              "Try pressing '/' inside this callout to add a heading or code block.",
+          },
+        ],
+      },
+      {
+        type: "paragraph",
+        content: "Press '/' anywhere to insert a new Callout.",
+      },
+      {
+        type: "paragraph",
+      },
+    ],
+  });
+
+  useEffect(() => setBlocks(editor.document), [editor]);
+
+  return (
+    <div className={"wrapper"}>
+      <div>BlockNote Editor:</div>
+      <div className={"item"}>
+        <BlockNoteView
+          editor={editor}
+          slashMenu={false}
+          onChange={() => {
+            setBlocks(editor.document);
+          }}
+        >
+          <SuggestionMenuController
+            triggerCharacter={"/"}
+            getItems={async (query) => {
+              const defaultItems = getDefaultReactSlashMenuItems(editor);
+              const lastBasicBlockIndex = defaultItems.findLastIndex(
+                (item) => item.group === "Basic blocks",
+              );
+              defaultItems.splice(
+                lastBasicBlockIndex + 1,
+                0,
+                insertCallout(editor),
+              );
+              return filterSuggestionItems(defaultItems, query);
+            }}
+          />
+        </BlockNoteView>
+      </div>
+      <div>Document JSON:</div>
+      <div className={"item bordered"}>
+        <pre>
+          <code>{JSON.stringify(blocks, null, 2)}</code>
+        </pre>
+      </div>
+    </div>
+  );
+}
diff --git a/examples/06-custom-schema/09-container-block/src/Callout.tsx b/examples/06-custom-schema/09-container-block/src/Callout.tsx
new file mode 100644
index 0000000000..3fb3a86da8
--- /dev/null
+++ b/examples/06-custom-schema/09-container-block/src/Callout.tsx
@@ -0,0 +1,102 @@
+import { createReactBlockSpec } from "@blocknote/react";
+import { MdCheckCircle, MdInfo, MdLightbulb, MdWarning } from "react-icons/md";
+
+import "./styles.css";
+
+// The flavors of callout the user can switch between.
+export const calloutTypes = [
+  { value: "tip", title: "Tip", icon: MdLightbulb },
+  { value: "info", title: "Info", icon: MdInfo },
+  { value: "warning", title: "Warning", icon: MdWarning },
+  { value: "success", title: "Success", icon: MdCheckCircle },
+] as const;
+
+// The Callout block. Declared with `content: "none"` plus the new
+// `children` config — the block hosts arbitrary child blocks in its body,
+// exposed at runtime as `block.children`.
+//
+// The callout's title demonstrates the complementary "string prop slot"
+// pattern: content that shouldn't be part of the rich-text document (no
+// formatting, comments, or multiplayer cursors needed) can live in a plain
+// string prop, edited through a regular <input> rendered inside the block.
+export const createCallout = createReactBlockSpec(
+  {
+    type: "callout",
+    propSchema: {
+      flavor: {
+        default: "tip",
+        values: ["tip", "info", "warning", "success"],
+      },
+      title: {
+        default: "",
+      },
+    },
+    content: "none",
+    children: {
+      min: 1,
+      default: [{ type: "paragraph" }],
+    },
+  },
+  {
+    render: (props) => {
+      const flavor =
+        calloutTypes.find((c) => c.value === props.block.props.flavor) ??
+        calloutTypes[0];
+      const Icon = flavor.icon;
+
+      const cycleFlavor = () => {
+        const idx = calloutTypes.findIndex(
+          (c) => c.value === props.block.props.flavor,
+        );
+        const next = calloutTypes[(idx + 1) % calloutTypes.length];
+        props.editor.updateBlock(props.block, {
+          type: "callout",
+          props: { flavor: next.value },
+        });
+      };
+
+      const commitTitle = (title: string) => {
+        if (title !== props.block.props.title) {
+          props.editor.updateBlock(props.block, {
+            type: "callout",
+            props: { title },
+          });
+        }
+      };
+
+      return (
+        <div className={"callout"}>
+          <button
+            className={"callout-icon-button"}
+            type={"button"}
+            contentEditable={false}
+            onClick={cycleFlavor}
+            aria-label={`Cycle callout flavor (current: ${flavor.title})`}
+            title={`Click to cycle flavor (current: ${flavor.title})`}
+          >
+            <Icon size={20} />
+          </button>
+          <div className={"callout-main"}>
+            {/* The title lives in a string prop, not in document content —
+                it's edited via a plain input. `contentEditable={false}` keeps
+                ProseMirror from treating typing here as document input. */}
+            <div className={"callout-title-wrapper"} contentEditable={false}>
+              <input
+                className={"callout-title-input"}
+                placeholder={"Add title"}
+                defaultValue={props.block.props.title}
+                onBlur={(event) => commitTitle(event.target.value)}
+                onKeyDown={(event) => {
+                  if (event.key === "Enter") {
+                    event.currentTarget.blur();
+                  }
+                }}
+              />
+            </div>
+            <div className={"callout-body"} ref={props.contentRef} />
+          </div>
+        </div>
+      );
+    },
+  },
+);
diff --git a/examples/06-custom-schema/09-container-block/src/styles.css b/examples/06-custom-schema/09-container-block/src/styles.css
new file mode 100644
index 0000000000..72d3d0283f
--- /dev/null
+++ b/examples/06-custom-schema/09-container-block/src/styles.css
@@ -0,0 +1,123 @@
+.wrapper {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+}
+
+.item {
+  border-radius: 0.5rem;
+  flex: 1;
+  overflow: hidden;
+}
+
+.item.bordered {
+  border: 1px solid gray;
+}
+
+.item pre {
+  border-radius: 0.5rem;
+  height: 100%;
+  overflow: auto;
+  padding-block: 1rem;
+  padding-inline: 54px;
+  width: 100%;
+  white-space: pre-wrap;
+}
+
+.callout {
+  display: flex;
+  align-items: flex-start;
+  gap: 12px;
+  flex-grow: 1;
+  border-radius: 6px;
+  padding: 12px 16px;
+  border-left: 4px solid var(--callout-accent, #888);
+  background-color: var(--callout-bg, #f3f4f6);
+}
+
+/* `tip` is the prop's default value, and BlockNote only writes a `data-*`
+   attribute for props that differ from their default — so a callout left on
+   `tip` carries no `data-flavor` at all. Style its absence alongside it. */
+.callout:not([data-flavor]),
+.callout[data-flavor="tip"] {
+  --callout-accent: #d97706;
+  --callout-bg: #fff7ed;
+}
+
+.callout[data-flavor="info"] {
+  --callout-accent: #507aff;
+  --callout-bg: #e6ebff;
+}
+
+.callout[data-flavor="warning"] {
+  --callout-accent: #b91c1c;
+  --callout-bg: #fef2f2;
+}
+
+.callout[data-flavor="success"] {
+  --callout-accent: #16a34a;
+  --callout-bg: #ecfdf5;
+}
+
+[data-color-scheme="dark"] .callout:not([data-flavor]),
+[data-color-scheme="dark"] .callout[data-flavor="tip"] {
+  --callout-bg: #432e0e;
+}
+
+[data-color-scheme="dark"] .callout[data-flavor="info"] {
+  --callout-bg: #1e2a5c;
+}
+
+[data-color-scheme="dark"] .callout[data-flavor="warning"] {
+  --callout-bg: #4a1212;
+}
+
+[data-color-scheme="dark"] .callout[data-flavor="success"] {
+  --callout-bg: #0d3b21;
+}
+
+.callout-icon-button {
+  background: none;
+  border: none;
+  cursor: pointer;
+  padding: 4px;
+  color: var(--callout-accent, #888);
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  margin-top: 2px;
+}
+
+.callout-icon-button:hover {
+  opacity: 0.75;
+}
+
+.callout-main {
+  flex-grow: 1;
+  min-width: 0;
+}
+
+.callout-title-wrapper {
+  margin-bottom: 4px;
+}
+
+.callout-title-input {
+  width: 100%;
+  border: none;
+  background: none;
+  outline: none;
+  font-weight: 600;
+  font-size: 1rem;
+  color: inherit;
+  padding: 0;
+}
+
+.callout-title-input::placeholder {
+  color: var(--callout-accent, #888);
+  opacity: 0.5;
+}
+
+.callout-body {
+  flex-grow: 1;
+  min-width: 0;
+}
diff --git a/examples/06-custom-schema/09-container-block/tsconfig.json b/examples/06-custom-schema/09-container-block/tsconfig.json
new file mode 100644
index 0000000000..93fa81bee8
--- /dev/null
+++ b/examples/06-custom-schema/09-container-block/tsconfig.json
@@ -0,0 +1,29 @@
+{
+  "__comment": "AUTO-GENERATED FILE, DO NOT EDIT DIRECTLY",
+  "compilerOptions": {
+    "target": "ESNext",
+    "useDefineForClassFields": true,
+    "lib": ["DOM", "DOM.Iterable", "ESNext"],
+    "allowJs": false,
+    "skipLibCheck": true,
+    "allowSyntheticDefaultImports": true,
+    "strict": true,
+    "forceConsistentCasingInFileNames": true,
+    "module": "ESNext",
+    "moduleResolution": "bundler",
+    "resolveJsonModule": true,
+    "isolatedModules": true,
+    "noEmit": true,
+    "jsx": "react-jsx",
+    "composite": true
+  },
+  "include": ["."],
+  "__ADD_FOR_LOCAL_DEV_references": [
+    {
+      "path": "../../../packages/core/"
+    },
+    {
+      "path": "../../../packages/react/"
+    }
+  ]
+}
diff --git a/examples/06-custom-schema/09-container-block/vite-env.d.ts b/examples/06-custom-schema/09-container-block/vite-env.d.ts
new file mode 100644
index 0000000000..bc2d8a36f3
--- /dev/null
+++ b/examples/06-custom-schema/09-container-block/vite-env.d.ts
@@ -0,0 +1 @@
+/// <reference types="vite-plus/client" />
diff --git a/examples/06-custom-schema/09-container-block/vite.config.ts b/examples/06-custom-schema/09-container-block/vite.config.ts
new file mode 100644
index 0000000000..0133a6da9e
--- /dev/null
+++ b/examples/06-custom-schema/09-container-block/vite.config.ts
@@ -0,0 +1,31 @@
+// AUTO-GENERATED FILE, DO NOT EDIT DIRECTLY
+import react from "@vitejs/plugin-react";
+import * as fs from "fs";
+import * as path from "path";
+import { defineConfig } from "vite-plus";
+// https://vitejs.dev/config/
+export default defineConfig(((conf: { command: string }) => ({
+  plugins: [react()],
+  optimizeDeps: {},
+  build: {
+    sourcemap: true,
+  },
+  resolve: {
+    alias:
+      conf.command === "build" ||
+      !fs.existsSync(path.resolve(__dirname, "../../packages/core/src"))
+        ? {}
+        : ({
+            // Comment out the lines below to load a built version of blocknote
+            // or, keep as is to load live from sources with live reload working
+            "@blocknote/core": path.resolve(
+              __dirname,
+              "../../packages/core/src/",
+            ),
+            "@blocknote/react": path.resolve(
+              __dirname,
+              "../../packages/react/src/",
+            ),
+          } as any),
+  },
+})) as Parameters<typeof defineConfig>[0]);
diff --git a/packages/core/package.json b/packages/core/package.json
index eb2700636d..8b9f1ee69b 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -72,6 +72,11 @@
       "import": "./dist/extensions.js",
       "require": "./dist/extensions.cjs"
     },
+    "./internal": {
+      "types": "./types/src/internal.d.ts",
+      "import": "./dist/internal.js",
+      "require": "./dist/internal.cjs"
+    },
     "./yjs": {
       "types": "./types/src/yjs/index.d.ts",
       "import": "./dist/yjs.js",
diff --git a/packages/core/src/api/blockManipulation/commands/insertBlocks/insertBlocks.ts b/packages/core/src/api/blockManipulation/commands/insertBlocks/insertBlocks.ts
index b41b268617..9e90e8e17f 100644
--- a/packages/core/src/api/blockManipulation/commands/insertBlocks/insertBlocks.ts
+++ b/packages/core/src/api/blockManipulation/commands/insertBlocks/insertBlocks.ts
@@ -1,4 +1,4 @@
-import { Fragment, Slice } from "prosemirror-model";
+import { Fragment, Node, NodeType, Slice } from "prosemirror-model";
 import type { Transaction } from "prosemirror-state";
 import { ReplaceStep } from "prosemirror-transform";
 import { Block, PartialBlock } from "../../../../blocks/defaultBlocks.js";
@@ -8,10 +8,93 @@ import {
   InlineContentSchema,
   StyleSchema,
 } from "../../../../schema/index.js";
+import { isContentContainerNode } from "../../../../schema/blocks/children.js";
 import { blockToNode } from "../../../nodeConversions/blockToNode.js";
 import { nodeToBlock } from "../../../nodeConversions/nodeToBlock.js";
 import { getNodeById } from "../../../nodeUtil.js";
 import { getPmSchema } from "../../../pmUtil.js";
+import {
+  descendToFirstInsertionPos,
+  descendToLastInsertionPos,
+} from "../../containers/containerNav.js";
+import { isContainerNode } from "../../containers/fixContainer.js";
+
+/**
+ * Where blocks go relative to a reference block. `"before"`/`"after"` make them
+ * siblings of it; `"start"`/`"end"` nest them inside it, as its first or last
+ * children.
+ *
+ * The nested placements are what addresses a container that has no children to
+ * point at — a `children: { min: 0 }` container that is currently empty has no
+ * child block to insert before or after.
+ */
+export type BlockPlacement = "before" | "after" | "start" | "end";
+
+/**
+ * Resolves a `placement` against a reference block into the document position
+ * a node of `nodeType` should be inserted at, or `null` when the reference
+ * block cannot take it there.
+ *
+ * Both insertion and the move commands ask this same question — "does this
+ * block fit here?" — so they ask it in one place. The answer comes from the
+ * schema's content matches rather than from a hand-written rule, so a
+ * container's `children` config is what decides it.
+ *
+ * `wrapIn` is set when the position only becomes valid once the nodes are
+ * wrapped: a regular block with no children yet has no `blockGroup` for them
+ * to go in, so one is created around them.
+ */
+export function getInsertionPos(
+  doc: Node,
+  reference: { node: Node; posBeforeNode: number },
+  placement: BlockPlacement,
+  nodeType: NodeType,
+): { pos: number; wrapIn?: NodeType } | null {
+  const { node, posBeforeNode } = reference;
+
+  if (placement === "before" || placement === "after") {
+    const pos =
+      placement === "before" ? posBeforeNode : posBeforeNode + node.nodeSize;
+    const $pos = doc.resolve(pos);
+
+    return $pos.parent.contentMatchAt($pos.index()).matchType(nodeType)
+      ? { pos }
+      : null;
+  }
+
+  // A container holds its children itself, or — when it has content of its own
+  // — in its generated `__children` node, which the descent helpers step into.
+  if (isContainerNode(node.type) || isContentContainerNode(node)) {
+    const pos =
+      placement === "start"
+        ? descendToFirstInsertionPos(node, posBeforeNode, nodeType)
+        : descendToLastInsertionPos(node, posBeforeNode, nodeType);
+
+    return pos === null ? null : { pos };
+  }
+
+  // A regular block keeps its children in a `blockGroup` that only exists once
+  // it has some.
+  const blockGroupType = nodeType.schema.nodes["blockGroup"];
+  if (node.type.name !== "blockContainer" || !blockGroupType) {
+    return null;
+  }
+
+  const blockGroupPos = posBeforeNode + 1 + node.firstChild!.nodeSize;
+
+  if (node.childCount < 2) {
+    return blockGroupType.contentMatch.matchType(nodeType)
+      ? { pos: blockGroupPos, wrapIn: blockGroupType }
+      : null;
+  }
+
+  const pos =
+    placement === "start"
+      ? descendToFirstInsertionPos(node.lastChild!, blockGroupPos, nodeType)
+      : descendToLastInsertionPos(node.lastChild!, blockGroupPos, nodeType);
+
+  return pos === null ? null : { pos };
+}
 
 export function insertBlocks<
   BSchema extends BlockSchema,
@@ -21,7 +104,7 @@ export function insertBlocks<
   tr: Transaction,
   blocksToInsert: PartialBlock<BSchema, I, S>[],
   referenceBlock: BlockIdentifier,
-  placement: "before" | "after" = "before",
+  placement: BlockPlacement = "before",
 ): Block<BSchema, I, S>[] {
   const id =
     typeof referenceBlock === "string" ? referenceBlock : referenceBlock.id;
@@ -37,14 +120,30 @@ export function insertBlocks<
     throw new Error(`Block with ID ${id} not found`);
   }
 
-  let pos = posInfo.posBeforeNode;
-  if (placement === "after") {
-    pos += posInfo.node.nodeSize;
+  if (nodesToInsert.length === 0) {
+    return [];
   }
 
-  tr.step(
-    new ReplaceStep(pos, pos, new Slice(Fragment.from(nodesToInsert), 0, 0)),
+  const target = getInsertionPos(
+    tr.doc,
+    posInfo,
+    placement,
+    nodesToInsert[0].type,
   );
+  if (!target) {
+    throw new Error(
+      `Cannot insert a block of type "${blocksToInsert[0].type ?? "paragraph"}" ` +
+        (placement === "before" || placement === "after"
+          ? `${placement} block with ID ${id}: its parent does not accept it.`
+          : `at the ${placement} of block with ID ${id}: the block does not accept it as a child.`),
+    );
+  }
+
+  const fragment = target.wrapIn
+    ? Fragment.from(target.wrapIn.create(null, nodesToInsert))
+    : Fragment.from(nodesToInsert);
+
+  tr.step(new ReplaceStep(target.pos, target.pos, new Slice(fragment, 0, 0)));
 
   // Now that the `PartialBlock`s have been converted to nodes, we can
   // re-convert them into full `Block`s.
diff --git a/packages/core/src/api/blockManipulation/commands/insertBlocks/insertPlacement.test.ts b/packages/core/src/api/blockManipulation/commands/insertBlocks/insertPlacement.test.ts
new file mode 100644
index 0000000000..27813aeef4
--- /dev/null
+++ b/packages/core/src/api/blockManipulation/commands/insertBlocks/insertPlacement.test.ts
@@ -0,0 +1,238 @@
+// @vitest-environment node
+import {
+  afterAll,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+} from "vite-plus/test";
+
+import { BlockNoteSchema } from "../../../../blocks/BlockNoteSchema.js";
+import { defaultBlockSpecs } from "../../../../blocks/defaultBlocks.js";
+import { BlockNoteEditor } from "../../../../editor/BlockNoteEditor.js";
+import { createBlockSpec } from "../../../../schema/blocks/createSpec.js";
+
+// These blocks are never rendered — the editor stays headless — so `render`
+// only has to exist for `createBlockSpec` to accept the spec.
+const container = (type: string, config: Record<string, unknown>) =>
+  createBlockSpec({ type, propSchema: {}, ...config } as any, {
+    render: () => {
+      throw new Error("not rendered in this suite");
+    },
+  })();
+
+const schema = BlockNoteSchema.create().extend({
+  blockSpecs: {
+    ...defaultBlockSpecs,
+    // The shape `"start"`/`"end"` exist for: a container that may legally hold
+    // nothing has no child block to address, so `"before"`/`"after"` cannot
+    // reach inside it.
+    box: container("box", { content: "none", children: { min: 0 } }),
+    titledBox: container("titledBox", {
+      content: "inline",
+      children: { min: 0 },
+    }),
+    // A container that only accepts other containers, so an insertion has to
+    // descend a level to find a place for a regular block.
+    grid: container("grid", {
+      content: "none",
+      children: { allow: { blocks: false, containers: ["cell"] }, min: 2 },
+    }),
+    cell: container("cell", {
+      content: "none",
+      children: {},
+      placement: "containerOnly",
+    }),
+    // A container that is full once it has one child.
+    single: container("single", { content: "none", children: { max: 1 } }),
+  } as const,
+});
+
+let editor: BlockNoteEditor<any, any, any>;
+
+beforeAll(() => {
+  editor = BlockNoteEditor.create({ schema }) as any;
+});
+
+afterAll(() => {
+  editor._tiptapEditor.destroy();
+  editor = undefined as any;
+});
+
+beforeEach(() => {
+  editor.replaceBlocks(editor.document, [
+    { id: "p-0", type: "paragraph", content: "Paragraph 0" },
+  ]);
+});
+
+describe('insertBlocks "start" / "end"', () => {
+  it("inserts into a childless container", () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "b-0", type: "box" },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+    expect(editor.getBlock("b-0")!.children).toHaveLength(0);
+
+    editor.insertBlocks(
+      [{ id: "inserted", type: "paragraph", content: "Inserted" }],
+      "b-0",
+      "end",
+    );
+
+    const box = editor.getBlock("b-0")!;
+    expect(box.children.map((child) => child.id)).toEqual(["inserted"]);
+  });
+
+  it('inserts into a childless container with "start"', () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "b-0", type: "box" },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    editor.insertBlocks(
+      [{ id: "inserted", type: "paragraph", content: "Inserted" }],
+      "b-0",
+      "start",
+    );
+
+    expect(editor.getBlock("b-0")!.children.map((child) => child.id)).toEqual([
+      "inserted",
+    ]);
+  });
+
+  it("prepends and appends around existing children", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        id: "b-0",
+        type: "box",
+        children: [{ id: "existing", type: "paragraph", content: "Existing" }],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    editor.insertBlocks([{ id: "first", type: "paragraph" }], "b-0", "start");
+    editor.insertBlocks([{ id: "last", type: "paragraph" }], "b-0", "end");
+
+    expect(editor.getBlock("b-0")!.children.map((child) => child.id)).toEqual([
+      "first",
+      "existing",
+      "last",
+    ]);
+  });
+
+  it("inserts into a childless container that has its own content", () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "t-0", type: "titledBox", content: "Title" },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+    expect(editor.getBlock("t-0")!.children).toHaveLength(0);
+
+    editor.insertBlocks([{ id: "first", type: "paragraph" }], "t-0", "start");
+    editor.insertBlocks([{ id: "last", type: "paragraph" }], "t-0", "end");
+
+    const toggle = editor.getBlock("t-0")!;
+    // The title is content, not a child — a nested insertion must not land
+    // in it, or before it.
+    expect(toggle.content).toEqual([
+      { type: "text", text: "Title", styles: {} },
+    ]);
+    expect(toggle.children.map((child) => child.id)).toEqual(["first", "last"]);
+  });
+
+  it("descends into a nested container that accepts the block", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        id: "g-0",
+        type: "grid",
+        children: [
+          { id: "c-0", type: "cell" },
+          { id: "c-1", type: "cell" },
+        ],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    // `grid` itself only accepts `cell`s, so both placements have to find the
+    // leading/trailing cell rather than giving up.
+    editor.insertBlocks([{ id: "first", type: "paragraph" }], "g-0", "start");
+    editor.insertBlocks([{ id: "last", type: "paragraph" }], "g-0", "end");
+
+    const grid = editor.getBlock("g-0")!;
+    expect(grid.children[0].children.map((child: any) => child.id)).toContain(
+      "first",
+    );
+    expect(grid.children[1].children.map((child: any) => child.id)).toContain(
+      "last",
+    );
+  });
+
+  it("nests under a regular block that has no children yet", () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "p-0", type: "paragraph", content: "Paragraph 0" },
+    ]);
+
+    editor.insertBlocks(
+      [{ id: "inserted", type: "paragraph", content: "Nested" }],
+      "p-0",
+      "end",
+    );
+
+    expect(editor.getBlock("p-0")!.children.map((child) => child.id)).toEqual([
+      "inserted",
+    ]);
+  });
+
+  it("nests under a regular block that already has children", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        id: "p-0",
+        type: "paragraph",
+        content: "Paragraph 0",
+        children: [{ id: "existing", type: "paragraph" }],
+      },
+    ]);
+
+    editor.insertBlocks([{ id: "first", type: "paragraph" }], "p-0", "start");
+
+    expect(editor.getBlock("p-0")!.children.map((child) => child.id)).toEqual([
+      "first",
+      "existing",
+    ]);
+  });
+
+  it("throws when the container has no room for the block", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        id: "s-0",
+        type: "single",
+        children: [{ id: "only", type: "paragraph" }],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    expect(() =>
+      editor.insertBlocks([{ type: "paragraph" }], "s-0", "end"),
+    ).toThrow(/does not accept it as a child/);
+  });
+
+  it("throws when a sibling placement isn't allowed either", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        id: "g-0",
+        type: "grid",
+        children: [
+          { id: "c-0", type: "cell" },
+          { id: "c-1", type: "cell" },
+        ],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    // `grid`'s children are `cell`s only, so a paragraph can't become one's
+    // sibling. Previously this surfaced as a raw ProseMirror `ReplaceError`.
+    expect(() =>
+      editor.insertBlocks([{ type: "paragraph" }], "c-0", "after"),
+    ).toThrow(/its parent does not accept it/);
+  });
+});
diff --git a/packages/core/src/api/blockManipulation/commands/mergeBlocks/mergeBlocks.ts b/packages/core/src/api/blockManipulation/commands/mergeBlocks/mergeBlocks.ts
index ce1a9455db..fe2a0b9dd6 100644
--- a/packages/core/src/api/blockManipulation/commands/mergeBlocks/mergeBlocks.ts
+++ b/packages/core/src/api/blockManipulation/commands/mergeBlocks/mergeBlocks.ts
@@ -1,5 +1,5 @@
 import { Node } from "prosemirror-model";
-import { EditorState } from "prosemirror-state";
+import { EditorState, TextSelection } from "prosemirror-state";
 
 import {
   BlockInfo,
@@ -91,7 +91,9 @@ export const getNextBlockInfo = (doc: Node, beforePos: number) => {
  * Then the bottom nested block returned is D.
  */
 export const getBottomNestedBlockInfo = (doc: Node, blockInfo: BlockInfo) => {
-  while (blockInfo.childContainer) {
+  // A container that allows zero children can have an empty child container,
+  // in which case the block itself is the bottom one.
+  while (blockInfo.childContainer && blockInfo.childContainer.node.childCount) {
     const group = blockInfo.childContainer.node;
 
     const newPos = doc
@@ -105,10 +107,10 @@ export const getBottomNestedBlockInfo = (doc: Node, blockInfo: BlockInfo) => {
 
 const canMerge = (prevBlockInfo: BlockInfo, nextBlockInfo: BlockInfo) => {
   return (
-    prevBlockInfo.isBlockContainer &&
+    prevBlockInfo.isWrappedBlock &&
     prevBlockInfo.blockContent.node.type.spec.content === "inline*" &&
     prevBlockInfo.blockContent.node.childCount > 0 &&
-    nextBlockInfo.isBlockContainer &&
+    nextBlockInfo.isWrappedBlock &&
     nextBlockInfo.blockContent.node.type.spec.content === "inline*"
   );
 };
@@ -120,7 +122,7 @@ const mergeBlocks = (
   nextBlockInfo: BlockInfo,
 ) => {
   // Un-nests all children of the next block.
-  if (!nextBlockInfo.isBlockContainer) {
+  if (!nextBlockInfo.isWrappedBlock) {
     throw new Error(
       `Attempted to merge block at position ${nextBlockInfo.bnBlock.beforePos} into previous block at position ${prevBlockInfo.bnBlock.beforePos}, but next block is not a block container`,
     );
@@ -147,13 +149,17 @@ const mergeBlocks = (
   // removing the closing tags of the first block and the opening tags of the
   // second one to stitch them together.
   if (dispatch) {
-    if (!prevBlockInfo.isBlockContainer) {
+    if (!prevBlockInfo.isWrappedBlock) {
       throw new Error(
         `Attempted to merge block at position ${nextBlockInfo.bnBlock.beforePos} into previous block at position ${prevBlockInfo.bnBlock.beforePos}, but previous block is not a block container`,
       );
     }
 
-    // TODO: test merging between a columnList and paragraph, between two columnLists, and v.v.
+    // Merging into or out of container blocks (columnLists, callouts, ...)
+    // is intentionally unsupported — `canMerge` refuses it above. The
+    // container-boundary Backspace/Delete branches in
+    // `KeyboardShortcutsExtension` handle those cases by moving blocks
+    // across the boundary instead of merging their content.
     dispatch(
       state.tr.delete(
         prevBlockInfo.blockContent.afterPos - 1,
@@ -165,6 +171,61 @@ const mergeBlocks = (
   return true;
 };
 
+/**
+ * Merges a container's first child into the container's own content — the
+ * Backspace-at-the-start-of-the-first-child case for a container that has a
+ * title of its own. The child's own children stay in the container, taking its
+ * place.
+ *
+ * Deliberately separate from `canMerge`/`mergeBlocks`: a *pure* container has
+ * no content to merge into, so those keep refusing container boundaries
+ * outright and the "move the block out" branch still handles them. Returns
+ * false — falling through to that branch — whenever either side isn't inline
+ * content.
+ */
+export const mergeIntoContainerContent = (
+  state: EditorState,
+  dispatch: ((args?: any) => any) | undefined,
+  containerInfo: BlockInfo,
+  childInfo: BlockInfo,
+) => {
+  if (!containerInfo.isWrappedBlock || !childInfo.isWrappedBlock) {
+    return false;
+  }
+
+  const title = containerInfo.blockContent;
+  const childContent = childInfo.blockContent;
+
+  if (
+    title.node.type.spec.content !== "inline*" ||
+    childContent.node.type.spec.content !== "inline*"
+  ) {
+    return false;
+  }
+
+  if (dispatch) {
+    const tr = state.tr;
+
+    // The title lies before the children, so none of these positions shift the
+    // ones used after them.
+    if (childInfo.childContainer?.node.childCount) {
+      tr.insert(
+        childInfo.bnBlock.afterPos,
+        childInfo.childContainer.node.content,
+      );
+    }
+    tr.delete(childInfo.bnBlock.beforePos, childInfo.bnBlock.afterPos);
+
+    const titleEndPos = title.afterPos - 1;
+    tr.insert(titleEndPos, childContent.node.content);
+    tr.setSelection(TextSelection.create(tr.doc, titleEndPos));
+
+    dispatch(tr);
+  }
+
+  return true;
+};
+
 export const mergeBlocksCommand =
   (posBetweenBlocks: number) =>
   ({
diff --git a/packages/core/src/api/blockManipulation/commands/moveBlocks/moveBlocks.test.ts b/packages/core/src/api/blockManipulation/commands/moveBlocks/moveBlocks.test.ts
index 61964a49ee..f034506f44 100644
--- a/packages/core/src/api/blockManipulation/commands/moveBlocks/moveBlocks.test.ts
+++ b/packages/core/src/api/blockManipulation/commands/moveBlocks/moveBlocks.test.ts
@@ -18,7 +18,7 @@ const getEditor = setupTestEnv();
 
 function makeSelectionSpanContent(selectionType: "text" | "node" | "cell") {
   const blockInfo = getEditor().transact((tr) => getBlockInfoFromSelection(tr));
-  if (!blockInfo.isBlockContainer) {
+  if (!blockInfo.isWrappedBlock) {
     throw new Error(
       `Selection points to a ${blockInfo.blockNoteType} node, not a blockContainer node`,
     );
diff --git a/packages/core/src/api/blockManipulation/commands/moveBlocks/moveBlocks.ts b/packages/core/src/api/blockManipulation/commands/moveBlocks/moveBlocks.ts
index 71598b7d69..46794bff7f 100644
--- a/packages/core/src/api/blockManipulation/commands/moveBlocks/moveBlocks.ts
+++ b/packages/core/src/api/blockManipulation/commands/moveBlocks/moveBlocks.ts
@@ -14,7 +14,8 @@ import {
   getNodeId,
 } from "../../../getBlockInfoFromPos.js";
 import { getNodeById } from "../../../nodeUtil.js";
-import { insertBlocks } from "../insertBlocks/insertBlocks.js";
+import { flattenNonInsertableBlocks } from "../../containers/fixContainer.js";
+import { getInsertionPos, insertBlocks } from "../insertBlocks/insertBlocks.js";
 import { removeAndInsertBlocks } from "../replaceBlocks/replaceBlocks.js";
 
 type BlockSelectionData = (
@@ -131,16 +132,6 @@ function updateBlockSelectionFromData(
   tr.setSelection(selection);
 }
 
-// Replaces top-level `column` blocks with their children, as a `column` is not
-// a valid block outside a `columnList`. Other blocks are returned as-is.
-function flattenColumns(
-  blocks: Block<any, any, any>[],
-): Block<any, any, any>[] {
-  return blocks.flatMap((block) =>
-    block.type === "column" ? block.children : [block],
-  );
-}
-
 /**
  * Removes the given blocks from the editor, then inserts them before/after a
  * reference block.
@@ -169,10 +160,12 @@ export function moveBlocks(
     // </column>
     // When the non-empty block is moved up, the column is seen as empty and
     // collapsed in the removal step, so the following insertion fails.
-    removeAndInsertBlocks(tr, blocks, [], { fixColumns: false });
+    removeAndInsertBlocks(tr, blocks, [], { fixContainers: false });
     insertBlocks<any, any, any>(
       tr,
-      flattenColumns(blocks),
+      // Blocks that can't stand on their own outside their container (e.g. a
+      // `column` outside its `columnList`) are replaced by their children.
+      flattenNonInsertableBlocks(blocks, editor.pmSchema),
       referenceBlock,
       placement,
     );
@@ -207,12 +200,33 @@ export function moveSelectedBlocksAndSelection(
   });
 }
 
-// Checks if a block is in a valid place after being moved. This check is
-// primitive at the moment and only returns false if the block's parent is a
-// `columnList` block. This is because regular blocks cannot be direct children
-// of `columnList` blocks.
-function checkPlacementIsValid(parentBlock?: Block<any, any, any>): boolean {
-  return !parentBlock || parentBlock.type !== "columnList";
+// Checks if a regular block would be in a valid place after being moved
+// before/after `referenceBlock`. A regular block nests under any non-container
+// block (it goes into that block's `blockGroup`), but a container block (e.g. a
+// `columnList`) only accepts what its content expression allows.
+//
+// Deferred to `getInsertionPos` so that "can a block go here?" has exactly one
+// answer, shared with `insertBlocks` — and so that it comes from the schema
+// rather than from a rule restated here.
+function checkPlacementIsValid(
+  editor: BlockNoteEditor<any, any, any>,
+  referenceBlock: Block<any, any, any>,
+  placement: "before" | "after",
+): boolean {
+  return editor.transact((tr) => {
+    const posInfo = getNodeById(referenceBlock.id, tr.doc);
+    if (!posInfo) {
+      return false;
+    }
+    return (
+      getInsertionPos(
+        tr.doc,
+        posInfo,
+        placement,
+        editor.pmSchema.nodes["blockContainer"],
+      ) !== null
+    );
+  });
 }
 
 // Gets the placement for moving a block up. This has 3 cases:
@@ -253,8 +267,8 @@ function getMoveUpPlacement(
     return undefined;
   }
 
-  const referenceBlockParent = editor.getParentBlock(referenceBlock);
-  if (!checkPlacementIsValid(referenceBlockParent)) {
+  if (!checkPlacementIsValid(editor, referenceBlock, placement)) {
+    const referenceBlockParent = editor.getParentBlock(referenceBlock);
     return getMoveUpPlacement(
       editor,
       placement === "after"
@@ -305,8 +319,8 @@ function getMoveDownPlacement(
     return undefined;
   }
 
-  const referenceBlockParent = editor.getParentBlock(referenceBlock);
-  if (!checkPlacementIsValid(referenceBlockParent)) {
+  if (!checkPlacementIsValid(editor, referenceBlock, placement)) {
+    const referenceBlockParent = editor.getParentBlock(referenceBlock);
     return getMoveDownPlacement(
       editor,
       placement === "before"
diff --git a/packages/core/src/api/blockManipulation/commands/nestBlock/nestBlock.ts b/packages/core/src/api/blockManipulation/commands/nestBlock/nestBlock.ts
index a0f76fdff0..a0a09d0099 100644
--- a/packages/core/src/api/blockManipulation/commands/nestBlock/nestBlock.ts
+++ b/packages/core/src/api/blockManipulation/commands/nestBlock/nestBlock.ts
@@ -19,9 +19,7 @@ function sinkItem(tr: Transaction, itemType: NodeType, groupType: NodeType) {
   const { $from, $to } = tr.selection;
   const range = $from.blockRange(
     $to,
-    (node) =>
-      node.childCount > 0 &&
-      (node.type.name === "blockGroup" || node.type.name === "column"), // change 1
+    (node) => node.childCount > 0 && node.type.isInGroup("childContainer"), // change 1
   );
   if (!range) {
     return false;
@@ -163,9 +161,7 @@ export function liftItem(
   const { $from, $to } = tr.selection;
   const range = $from.blockRange(
     $to,
-    (node) =>
-      node.childCount > 0 &&
-      (node.type.name === "blockGroup" || node.type.name === "column"), // change 1
+    (node) => node.childCount > 0 && node.type.isInGroup("childContainer"), // change 1
   );
   if (!range) {
     return false;
@@ -195,14 +191,36 @@ export function canNestBlock(editor: BlockNoteEditor<any, any, any>) {
   return editor.transact((tr) => {
     const { bnBlock: blockContainer } = getBlockInfoFromSelection(tr);
 
-    return tr.doc.resolve(blockContainer.beforePos).nodeBefore !== null;
+    // Mirrors `sinkItem`'s precondition: nesting is only possible under a
+    // previous sibling that is itself a `blockContainer`. (A previous sibling
+    // of another type — e.g. a container block — made this return true while
+    // `nestBlock` did nothing.)
+    return (
+      tr.doc.resolve(blockContainer.beforePos).nodeBefore?.type ===
+      editor.pmSchema.nodes["blockContainer"]
+    );
   });
 }
 
 export function canUnnestBlock(editor: BlockNoteEditor<any, any, any>) {
   return editor.transact((tr) => {
-    const { bnBlock: blockContainer } = getBlockInfoFromSelection(tr);
+    const { $from, $to } = tr.selection;
+
+    // Mirrors `liftItem`'s preconditions instead of approximating with
+    // depth — a block whose depth > 1 because it sits inside a container
+    // (e.g. a column) is not un-nestable, only a block nested under another
+    // `blockContainer` is.
+    const range = $from.blockRange(
+      $to,
+      (node) => node.childCount > 0 && node.type.isInGroup("childContainer"),
+    );
+    if (!range) {
+      return false;
+    }
 
-    return tr.doc.resolve(blockContainer.beforePos).depth > 1;
+    return (
+      $from.node(range.depth - 1).type ===
+      editor.pmSchema.nodes["blockContainer"]
+    );
   });
 }
diff --git a/packages/core/src/api/blockManipulation/commands/replaceBlocks/replaceBlocks.ts b/packages/core/src/api/blockManipulation/commands/replaceBlocks/replaceBlocks.ts
index d9e1e72981..84be8fa9fc 100644
--- a/packages/core/src/api/blockManipulation/commands/replaceBlocks/replaceBlocks.ts
+++ b/packages/core/src/api/blockManipulation/commands/replaceBlocks/replaceBlocks.ts
@@ -11,7 +11,8 @@ import type {
 import { blockToNode } from "../../../nodeConversions/blockToNode.js";
 import { nodeToBlock } from "../../../nodeConversions/nodeToBlock.js";
 import { getPmSchema } from "../../../pmUtil.js";
-import { fixColumnList } from "./util/fixColumnList.js";
+import { fixContainersById } from "../../containers/fixContainer.js";
+import { getAncestorContainers } from "../../containers/containerNav.js";
 
 export function removeAndInsertBlocks<
   BSchema extends BlockSchema,
@@ -22,7 +23,7 @@ export function removeAndInsertBlocks<
   blocksToRemove: BlockIdentifier[],
   blocksToInsert: PartialBlock<BSchema, I, S>[],
   options: {
-    fixColumns?: boolean;
+    fixContainers?: boolean;
   } = {},
 ): {
   insertedBlocks: Block<BSchema, I, S>[];
@@ -43,7 +44,10 @@ export function removeAndInsertBlocks<
     ),
   );
   const removedBlocks: Block<BSchema, I, S>[] = [];
-  const columnListPositions = new Set<number>();
+  // Ancestor containers of removed blocks, to repair afterwards. Tracked by
+  // node id (not position) since the removals — and earlier repairs — shift
+  // positions; recorded with their depth so repairs run deepest-first.
+  const containersToFix: { id: string; depth: number }[] = [];
 
   const idOfFirstBlock =
     typeof blocksToRemove[0] === "string"
@@ -84,10 +88,10 @@ export function removeAndInsertBlocks<
 
     const $pos = tr.doc.resolve(pos - removedSize);
 
-    if ($pos.node().type.name === "column") {
-      columnListPositions.add($pos.before(-1));
-    } else if ($pos.node().type.name === "columnList") {
-      columnListPositions.add($pos.before());
+    for (const container of getAncestorContainers($pos.doc, $pos.pos)) {
+      if (!containersToFix.some((c) => c.id === container.id)) {
+        containersToFix.push(container);
+      }
     }
 
     if (
@@ -119,11 +123,12 @@ export function removeAndInsertBlocks<
     );
   }
 
-  // Collapses empty columns/columnLists. Callers where the removal isn't a
-  // deletion can opt out - e.g. `moveBlocks` re-inserts the blocks elsewhere
-  // and deliberately leaves emptied columns as-is.
-  if (options.fixColumns !== false) {
-    columnListPositions.forEach((pos) => fixColumnList(tr, pos));
+  // Repairs the containers the removed blocks lived in (e.g. collapses
+  // emptied columns/columnLists), deepest-first. Callers where the removal
+  // isn't a deletion can opt out - e.g. `moveBlocks` re-inserts the blocks
+  // elsewhere and deliberately leaves emptied containers as-is.
+  if (options.fixContainers !== false) {
+    fixContainersById(tr, containersToFix);
   }
 
   // Converts the nodes created from `blocksToInsert` into full `Block`s.
diff --git a/packages/core/src/api/blockManipulation/commands/replaceBlocks/util/fixColumnList.ts b/packages/core/src/api/blockManipulation/commands/replaceBlocks/util/fixColumnList.ts
deleted file mode 100644
index 3097851f47..0000000000
--- a/packages/core/src/api/blockManipulation/commands/replaceBlocks/util/fixColumnList.ts
+++ /dev/null
@@ -1,173 +0,0 @@
-import { Slice, type Node } from "prosemirror-model";
-import { type Transaction } from "prosemirror-state";
-import { ReplaceAroundStep } from "prosemirror-transform";
-
-/**
- * Checks if a `column` node is empty, i.e. if it has only a single empty
- * paragraph.
- * @param column The column to check.
- * @returns Whether the column is empty.
- */
-export function isEmptyColumn(column: Node) {
-  if (!column || column.type.name !== "column") {
-    throw new Error("Invalid columnPos: does not point to column node.");
-  }
-
-  const blockContainer = column.firstChild;
-  if (!blockContainer) {
-    throw new Error("Invalid column: does not have child node.");
-  }
-
-  const blockContent = blockContainer.firstChild;
-  if (!blockContent) {
-    throw new Error("Invalid blockContainer: does not have child node.");
-  }
-
-  return (
-    column.childCount === 1 &&
-    blockContainer.childCount === 1 &&
-    blockContent.type.name === "paragraph" &&
-    blockContent.content.content.length === 0
-  );
-}
-
-/**
- * Removes all empty `column` nodes in a `columnList`. A `column` node is empty
- * if it has only a single empty block. If, however, removing the `column`s
- * leaves the `columnList` that has fewer than two, ProseMirror will re-add
- * empty columns.
- * @param tr The `Transaction` to add the changes to.
- * @param columnListPos The position just before the `columnList` node.
- */
-export function removeEmptyColumns(tr: Transaction, columnListPos: number) {
-  const $columnListPos = tr.doc.resolve(columnListPos);
-  const columnList = $columnListPos.nodeAfter;
-  if (!columnList || columnList.type.name !== "columnList") {
-    throw new Error(
-      "Invalid columnListPos: does not point to columnList node.",
-    );
-  }
-
-  for (
-    let columnIndex = columnList.childCount - 1;
-    columnIndex >= 0;
-    columnIndex--
-  ) {
-    const columnPos = tr.doc
-      .resolve($columnListPos.pos + 1)
-      .posAtIndex(columnIndex);
-    const $columnPos = tr.doc.resolve(columnPos);
-    const column = $columnPos.nodeAfter;
-    if (!column || column.type.name !== "column") {
-      throw new Error("Invalid columnPos: does not point to column node.");
-    }
-
-    if (isEmptyColumn(column)) {
-      tr.delete(columnPos, columnPos + column.nodeSize);
-    }
-  }
-}
-
-/**
- * Fixes potential issues in a `columnList` node after a
- * `blockContainer`/`column` node is (re)moved from it:
- *
- * - Removes all empty `column` nodes. A `column` node is empty if it has only
- * a single empty block.
- * - If all but one `column` nodes are empty, replaces the `columnList` with
- * the content of the non-empty `column`.
- * - If all `column` nodes are empty, removes the `columnList` entirely.
- * @param tr The `Transaction` to add the changes to.
- * @param columnListPos
- * @returns The position just before the `columnList` node.
- */
-export function fixColumnList(tr: Transaction, columnListPos: number) {
-  removeEmptyColumns(tr, columnListPos);
-
-  const $columnListPos = tr.doc.resolve(columnListPos);
-  const columnList = $columnListPos.nodeAfter;
-  if (!columnList || columnList.type.name !== "columnList") {
-    throw new Error(
-      "Invalid columnListPos: does not point to columnList node.",
-    );
-  }
-
-  if (columnList.childCount > 2) {
-    // Do nothing if the `columnList` has more than two non-empty `column`s. In
-    // the case that the `columnList` has exactly two columns, we may need to
-    // still remove it, as it's possible that one or both columns are empty.
-    // This is because after `removeEmptyColumns` is called, if the
-    // `columnList` has fewer than two `column`s, ProseMirror will re-add empty
-    // `column`s until there are two total, in order to fit the schema.
-    return;
-  }
-
-  if (columnList.childCount < 2) {
-    // Throw an error if the `columnList` has fewer than two columns. After
-    // `removeEmptyColumns` is called, if the `columnList` has fewer than two
-    // `column`s, ProseMirror will re-add empty `column`s until there are two
-    // total, in order to fit the schema. So if there are fewer than two here,
-    // either the schema, or ProseMirror's internals, must have changed.
-    throw new Error("Invalid columnList: contains fewer than two children.");
-  }
-
-  const firstColumnBeforePos = columnListPos + 1;
-  const $firstColumnBeforePos = tr.doc.resolve(firstColumnBeforePos);
-  const firstColumn = $firstColumnBeforePos.nodeAfter;
-
-  const lastColumnAfterPos = columnListPos + columnList.nodeSize - 1;
-  const $lastColumnAfterPos = tr.doc.resolve(lastColumnAfterPos);
-  const lastColumn = $lastColumnAfterPos.nodeBefore;
-
-  if (!firstColumn || !lastColumn) {
-    throw new Error("Invalid columnList: does not contain children.");
-  }
-
-  const firstColumnEmpty = isEmptyColumn(firstColumn);
-  const lastColumnEmpty = isEmptyColumn(lastColumn);
-
-  if (firstColumnEmpty && lastColumnEmpty) {
-    // Removes `columnList`
-    tr.delete(columnListPos, columnListPos + columnList.nodeSize);
-
-    return;
-  }
-
-  if (firstColumnEmpty) {
-    tr.step(
-      new ReplaceAroundStep(
-        // Replaces `columnList`.
-        columnListPos,
-        columnListPos + columnList.nodeSize,
-        // Replaces with content of last `column`.
-        lastColumnAfterPos - lastColumn.nodeSize + 1,
-        lastColumnAfterPos - 1,
-        // Doesn't append anything.
-        Slice.empty,
-        0,
-        false,
-      ),
-    );
-
-    return;
-  }
-
-  if (lastColumnEmpty) {
-    tr.step(
-      new ReplaceAroundStep(
-        // Replaces `columnList`.
-        columnListPos,
-        columnListPos + columnList.nodeSize,
-        // Replaces with content of first `column`.
-        firstColumnBeforePos + 1,
-        firstColumnBeforePos + firstColumn.nodeSize - 1,
-        // Doesn't append anything.
-        Slice.empty,
-        0,
-        false,
-      ),
-    );
-
-    return;
-  }
-}
diff --git a/packages/core/src/api/blockManipulation/commands/splitBlock/splitBlock.test.ts b/packages/core/src/api/blockManipulation/commands/splitBlock/splitBlock.test.ts
index ab02a865f0..9a83857cd1 100644
--- a/packages/core/src/api/blockManipulation/commands/splitBlock/splitBlock.test.ts
+++ b/packages/core/src/api/blockManipulation/commands/splitBlock/splitBlock.test.ts
@@ -35,7 +35,7 @@ function setSelectionWithOffset(
 
   const info = getBlockInfo(posInfo);
 
-  if (!info.isBlockContainer) {
+  if (!info.isWrappedBlock) {
     throw new Error("Target block is not a block container");
   }
 
diff --git a/packages/core/src/api/blockManipulation/commands/splitBlock/splitBlock.ts b/packages/core/src/api/blockManipulation/commands/splitBlock/splitBlock.ts
index 1e73471d23..ef74f8e898 100644
--- a/packages/core/src/api/blockManipulation/commands/splitBlock/splitBlock.ts
+++ b/packages/core/src/api/blockManipulation/commands/splitBlock/splitBlock.ts
@@ -36,7 +36,7 @@ export const splitBlockTr = (
 
   const info = getBlockInfo(nearestBlockContainerPos);
 
-  if (!info.isBlockContainer) {
+  if (!info.isWrappedBlock) {
     return false;
   }
   const schema = getPmSchema(tr);
diff --git a/packages/core/src/api/blockManipulation/commands/updateBlock/updateBlock.test.ts b/packages/core/src/api/blockManipulation/commands/updateBlock/updateBlock.test.ts
index e44e4a6380..c695de98ae 100644
--- a/packages/core/src/api/blockManipulation/commands/updateBlock/updateBlock.test.ts
+++ b/packages/core/src/api/blockManipulation/commands/updateBlock/updateBlock.test.ts
@@ -181,7 +181,7 @@ describe("Test updateBlock", () => {
       getNodeById("heading-with-everything", getEditor().prosemirrorState.doc)!,
     );
 
-    if (!info.isBlockContainer) {
+    if (!info.isWrappedBlock) {
       throw new Error("heading-with-everything is not a block container");
     }
 
@@ -210,7 +210,7 @@ describe("Test updateBlock", () => {
       getNodeById("heading-with-everything", getEditor().prosemirrorState.doc)!,
     );
 
-    if (!info.isBlockContainer) {
+    if (!info.isWrappedBlock) {
       throw new Error("heading-with-everything is not a block container");
     }
 
@@ -240,7 +240,7 @@ describe("Test updateBlock", () => {
       getNodeById("heading-with-everything", getEditor().prosemirrorState.doc)!,
     );
 
-    if (!info.isBlockContainer) {
+    if (!info.isWrappedBlock) {
       throw new Error("heading-with-everything is not a block container");
     }
 
@@ -273,7 +273,7 @@ describe("Test updateBlock", () => {
       getNodeById("table-0", getEditor().prosemirrorState.doc)!,
     );
 
-    if (!info.isBlockContainer) {
+    if (!info.isWrappedBlock) {
       throw new Error("table-0 is not a block container");
     }
 
@@ -303,7 +303,7 @@ describe("Test updateBlock", () => {
       getNodeById("table-0", getEditor().prosemirrorState.doc)!,
     );
 
-    if (!info.isBlockContainer) {
+    if (!info.isWrappedBlock) {
       throw new Error("table-0 is not a block container");
     }
 
@@ -940,7 +940,7 @@ describe("Test updateBlock minimal steps", () => {
         editor.prosemirrorState.doc,
       )!,
     );
-    if (!info.isBlockContainer) {
+    if (!info.isWrappedBlock) {
       throw new Error("paragraph-with-styled-content is not a block container");
     }
 
diff --git a/packages/core/src/api/blockManipulation/commands/updateBlock/updateBlock.ts b/packages/core/src/api/blockManipulation/commands/updateBlock/updateBlock.ts
index 6edfc434d5..5ebc4a619e 100644
--- a/packages/core/src/api/blockManipulation/commands/updateBlock/updateBlock.ts
+++ b/packages/core/src/api/blockManipulation/commands/updateBlock/updateBlock.ts
@@ -2,6 +2,7 @@ import {
   Fragment,
   type NodeType,
   type Node as PMNode,
+  type Schema,
   Slice,
 } from "prosemirror-model";
 import { TextSelection, Transaction } from "prosemirror-state";
@@ -27,7 +28,12 @@ import {
 } from "../../../nodeConversions/blockToNode.js";
 import { nodeToBlock } from "../../../nodeConversions/nodeToBlock.js";
 import { getNodeById } from "../../../nodeUtil.js";
-import { getPmSchema } from "../../../pmUtil.js";
+import { getBlockSchema, getPmSchema } from "../../../pmUtil.js";
+import {
+  getContentContainerNodeTypes,
+  isContainerType,
+  isContentContainerNode,
+} from "../../../../schema/blocks/children.js";
 
 // for compatibility with tiptap. TODO: remove as we want to remove dependency on tiptap command interface
 export const updateBlockCommand = <
@@ -82,40 +88,75 @@ export function updateBlockTr<
 
   // Adds blockGroup node with child blocks if necessary.
 
-  const oldNodeType = pmSchema.nodes[blockInfo.blockNoteType];
-  const newNodeType = pmSchema.nodes[block.type || blockInfo.blockNoteType];
+  const newBlockType = block.type || blockInfo.blockNoteType;
+  const newNodeType = pmSchema.nodes[newBlockType];
   const newBnBlockNodeType = newNodeType.isInGroup("bnBlock")
     ? newNodeType
     : pmSchema.nodes["blockContainer"];
 
-  if (blockInfo.isBlockContainer && newNodeType.isInGroup("blockContent")) {
-    const replaceFromOffset =
-      replaceFromPos !== undefined &&
-      replaceFromPos > blockInfo.blockContent.beforePos &&
-      replaceFromPos < blockInfo.blockContent.afterPos
-        ? replaceFromPos - blockInfo.blockContent.beforePos - 1
-        : undefined;
-
-    const replaceToOffset =
-      replaceToPos !== undefined &&
-      replaceToPos > blockInfo.blockContent.beforePos &&
-      replaceToPos < blockInfo.blockContent.afterPos
-        ? replaceToPos - blockInfo.blockContent.beforePos - 1
-        : undefined;
+  // The dispatch below is about *content* nodes, not block nodes. A container
+  // with its own content keeps that content in a generated node rather than in
+  // its own, so routing on the block's node type would send an update of its
+  // content to the full-replace arm — where it used to be silently dropped.
+  const isContentContainer = isContentContainerNode(blockInfo.bnBlock.node);
+
+  const replaceFromOffset =
+    blockInfo.blockContent &&
+    replaceFromPos !== undefined &&
+    replaceFromPos > blockInfo.blockContent.beforePos &&
+    replaceFromPos < blockInfo.blockContent.afterPos
+      ? replaceFromPos - blockInfo.blockContent.beforePos - 1
+      : undefined;
+
+  const replaceToOffset =
+    blockInfo.blockContent &&
+    replaceToPos !== undefined &&
+    replaceToPos > blockInfo.blockContent.beforePos &&
+    replaceToPos < blockInfo.blockContent.afterPos
+      ? replaceToPos - blockInfo.blockContent.beforePos - 1
+      : undefined;
 
+  if (
+    blockInfo.isWrappedBlock &&
+    blockInfo.bnBlock.node.type.name === "blockContainer" &&
+    newNodeType.isInGroup("blockContent")
+  ) {
     updateChildren(block, tr, blockInfo);
     // The code below determines the new content of the block.
     // or "keep" to keep as-is
     updateBlockContentNode(
       block,
       tr,
-      oldNodeType,
+      pmSchema.nodes[blockInfo.blockNoteType],
       newNodeType,
       blockInfo,
       replaceFromOffset,
       replaceToOffset,
     );
-  } else if (!blockInfo.isBlockContainer && newNodeType.isInGroup("bnBlock")) {
+  } else if (
+    blockInfo.isWrappedBlock &&
+    isContentContainer &&
+    newBlockType === blockInfo.blockNoteType
+  ) {
+    // Same container, so its generated content node stays as it is — only what
+    // that node holds may change.
+    const contentNodeType = blockInfo.blockContent.node.type;
+
+    updateChildren(block, tr, blockInfo);
+    updateBlockContentNode(
+      block,
+      tr,
+      contentNodeType,
+      contentNodeType,
+      blockInfo,
+      replaceFromOffset,
+      replaceToOffset,
+    );
+  } else if (
+    !blockInfo.isWrappedBlock &&
+    newNodeType.isInGroup("bnBlock") &&
+    !getContentContainerNodeTypes(pmSchema, newBlockType)
+  ) {
     updateChildren(block, tr, blockInfo);
     // old node was a bnBlock type (like column or columnList) and new block as well
     // No op, we just update the bnBlock below (at end of function) and have already updated the children
@@ -128,9 +169,21 @@ export function updateBlockTr<
     // for this, we do a nodeToBlock on the existing block to get the children.
     // it would be cleaner to use a ReplaceAroundStep, but this is a bit simpler and it's quite an edge case
     const existingBlock = nodeToBlock(blockInfo.bnBlock.node, tr.doc);
+    const carried = carryOverContent(
+      existingBlock.content,
+      newBlockType,
+      pmSchema,
+    );
+    // If no children are passed in, use the existing block's — but only when
+    // there actually are some. `nodeToBlock` always emits an array, and an
+    // empty one would read as "explicitly childless", suppressing the seeding a
+    // container needs when converting from a childless block.
+    const children = [...carried.children, ...existingBlock.children];
+
     const replacementNode = blockToNode(
       {
-        children: existingBlock.children, // if no children are passed in, use existing children
+        ...(carried.content ? { content: carried.content } : {}),
+        ...(children.length > 0 ? { children } : {}),
         ...block,
       },
       pmSchema,
@@ -158,6 +211,41 @@ export function updateBlockTr<
   }
 }
 
+function carryOverContent(
+  existingContent: Block<any, any, any>["content"],
+  newBlockType: string,
+  pmSchema: Schema,
+): {
+  content?: PartialBlock<any, any, any>["content"];
+  children: PartialBlock<any, any, any>[];
+} {
+  const nothing = { children: [] };
+
+  if (!existingContent || !Array.isArray(existingContent)) {
+    return nothing;
+  }
+  if (existingContent.length === 0) {
+    return nothing;
+  }
+
+  const targetConfig = getBlockSchema(pmSchema)[newBlockType];
+  if (!targetConfig) {
+    return nothing;
+  }
+
+  if (targetConfig.content === "inline" || targetConfig.content === "plain") {
+    return { content: existingContent, children: [] };
+  }
+
+  if (targetConfig.content === "none" && isContainerType(targetConfig)) {
+    return {
+      children: [{ type: "paragraph", content: existingContent } as any],
+    };
+  }
+
+  return nothing;
+}
+
 function updateBlockContentNode<
   BSchema extends BlockSchema,
   I extends InlineContentSchema,
@@ -521,7 +609,7 @@ function updateChildren<
         Fragment.from(childNodes),
       );
     } else {
-      if (!blockInfo.isBlockContainer) {
+      if (!blockInfo.isWrappedBlock) {
         throw new Error("impossible");
       }
       // Inserts a new blockGroup containing the child nodes created earlier.
@@ -637,7 +725,7 @@ function restoreCellAnchor(
   // 1) Resolve the table node in the current document
   let tablePos = -1;
 
-  if (blockInfo.isBlockContainer) {
+  if (blockInfo.isWrappedBlock) {
     // Prefer the blockContent position when available (points directly at the PM table node)
     tablePos = tr.mapping.map(blockInfo.blockContent.beforePos);
   } else {
diff --git a/packages/core/src/api/blockManipulation/containers/__snapshots__/containers.test.ts.snap b/packages/core/src/api/blockManipulation/containers/__snapshots__/containers.test.ts.snap
new file mode 100644
index 0000000000..f8e3f971e1
--- /dev/null
+++ b/packages/core/src/api/blockManipulation/containers/__snapshots__/containers.test.ts.snap
@@ -0,0 +1,34 @@
+// Vitest Snapshot v1, https://vitest.dev/guide/snapshot.html
+
+exports[`children repair > unwraps a repair-configured container when only one non-empty child remains 1`] = `
+[
+  {
+    "children": [],
+    "content": [
+      {
+        "styles": {},
+        "text": "B",
+        "type": "text",
+      },
+    ],
+    "id": "cell-b-p",
+    "props": {
+      "backgroundColor": "default",
+      "textAlignment": "left",
+      "textColor": "default",
+    },
+    "type": "paragraph",
+  },
+  {
+    "children": [],
+    "content": [],
+    "id": "trailing",
+    "props": {
+      "backgroundColor": "default",
+      "textAlignment": "left",
+      "textColor": "default",
+    },
+    "type": "paragraph",
+  },
+]
+`;
diff --git a/packages/core/src/api/blockManipulation/containers/containerNav.ts b/packages/core/src/api/blockManipulation/containers/containerNav.ts
new file mode 100644
index 0000000000..a7cd2df4b7
--- /dev/null
+++ b/packages/core/src/api/blockManipulation/containers/containerNav.ts
@@ -0,0 +1,108 @@
+import type { Node, NodeType } from "prosemirror-model";
+
+import { isContentContainerNode } from "../../../schema/blocks/children.js";
+import { isContainerNode } from "./fixContainer.js";
+
+export function descendToLastInsertionPos(
+  container: Node,
+  containerBeforePos: number,
+  nodeType: NodeType,
+): number | null {
+  const endPos = containerBeforePos + 1 + container.content.size;
+  if (container.contentMatchAt(container.childCount).matchType(nodeType)) {
+    return endPos;
+  }
+  const lastChild = container.lastChild;
+  if (lastChild && isContainerNode(lastChild.type)) {
+    return descendToLastInsertionPos(
+      lastChild,
+      endPos - lastChild.nodeSize,
+      nodeType,
+    );
+  }
+  return null;
+}
+
+export function descendToFirstInsertionPos(
+  container: Node,
+  containerBeforePos: number,
+  nodeType: NodeType,
+): number | null {
+  // A content container's children start after the content node.
+  if (isContentContainerNode(container)) {
+    return descendToFirstInsertionPos(
+      container.lastChild!,
+      containerBeforePos + 1 + container.firstChild!.nodeSize,
+      nodeType,
+    );
+  }
+
+  const startPos = containerBeforePos + 1;
+  if (container.contentMatchAt(0).matchType(nodeType)) {
+    return startPos;
+  }
+  const firstChild = container.firstChild;
+  if (firstChild && isContainerNode(firstChild.type)) {
+    return descendToFirstInsertionPos(firstChild, startPos, nodeType);
+  }
+  return null;
+}
+
+export function getFirstLeafBlock(
+  container: Node,
+  containerBeforePos: number,
+): { node: Node; beforePos: number } | null {
+  if (isContentContainerNode(container)) {
+    return getFirstLeafBlock(
+      container.lastChild!,
+      containerBeforePos + 1 + container.firstChild!.nodeSize,
+    );
+  }
+
+  const firstChild = container.firstChild;
+  if (!firstChild) {
+    return null;
+  }
+  const firstChildBeforePos = containerBeforePos + 1;
+  if (isContainerNode(firstChild.type)) {
+    return getFirstLeafBlock(firstChild, firstChildBeforePos);
+  }
+  return { node: firstChild, beforePos: firstChildBeforePos };
+}
+
+export function ascendToInsertablePos(
+  doc: Node,
+  pos: number,
+  nodeType: NodeType,
+): number | null {
+  for (;;) {
+    const $pos = doc.resolve(pos);
+    const parent = $pos.node();
+    if (parent.contentMatchAt($pos.index()).matchType(nodeType)) {
+      return pos;
+    }
+    if (isContainerNode(parent.type) && $pos.depth > 0) {
+      pos = $pos.before();
+      continue;
+    }
+    return null;
+  }
+}
+
+export function getAncestorContainers(
+  doc: Node,
+  pos: number,
+): { id: string; depth: number }[] {
+  const $pos = doc.resolve(pos);
+  const containers: { id: string; depth: number }[] = [];
+  for (let depth = $pos.depth; depth > 0; depth--) {
+    const ancestor = $pos.node(depth);
+    if (
+      (isContainerNode(ancestor.type) || isContentContainerNode(ancestor)) &&
+      ancestor.attrs.id
+    ) {
+      containers.push({ id: ancestor.attrs.id, depth });
+    }
+  }
+  return containers;
+}
diff --git a/packages/core/src/api/blockManipulation/containers/containerUI.ts b/packages/core/src/api/blockManipulation/containers/containerUI.ts
new file mode 100644
index 0000000000..b4633d5ead
--- /dev/null
+++ b/packages/core/src/api/blockManipulation/containers/containerUI.ts
@@ -0,0 +1,61 @@
+import type { BlockNoteEditor } from "../../../editor/BlockNoteEditor.js";
+import { isContainerType } from "../../../schema/blocks/children.js";
+
+export type ContainerUIInfo = {
+  containerTypes: ReadonlySet<string>;
+  draggableContainerTypes: ReadonlySet<string>;
+  /**
+   * Regular (non-container) block types whose spec sets `meta.draggable:
+   * false`. Container types are tracked separately in
+   * `draggableContainerTypes`, because they're identified in the DOM by
+   * `data-node-type` while regular blocks all share the `blockContainer` node
+   * and are identified by their content's `data-content-type`.
+   */
+  nonDraggableBlockTypes: ReadonlySet<string>;
+  containerSelector: string | null;
+};
+
+function buildSelector(types: ReadonlySet<string>): string | null {
+  if (types.size === 0) {
+    return null;
+  }
+  return [...types].map((type) => `[data-node-type="${type}"]`).join(",");
+}
+
+export function getContainerUIInfo(
+  editor: Pick<BlockNoteEditor<any, any, any>, "schema">,
+): ContainerUIInfo {
+  const containerTypes = new Set<string>();
+  const draggableContainerTypes = new Set<string>();
+  const nonDraggableBlockTypes = new Set<string>();
+
+  for (const [type, spec] of Object.entries(
+    editor.schema.blockSpecs as Record<
+      string,
+      {
+        config: any;
+        implementation?: { meta?: { draggable?: boolean } };
+      }
+    >,
+  )) {
+    const draggable = spec.implementation?.meta?.draggable !== false;
+
+    if (!isContainerType(spec.config)) {
+      if (!draggable) {
+        nonDraggableBlockTypes.add(type);
+      }
+      continue;
+    }
+    containerTypes.add(type);
+    if (draggable) {
+      draggableContainerTypes.add(type);
+    }
+  }
+
+  return {
+    containerTypes,
+    draggableContainerTypes,
+    nonDraggableBlockTypes,
+    containerSelector: buildSelector(containerTypes),
+  };
+}
diff --git a/packages/core/src/api/blockManipulation/containers/containers.browser.test.ts b/packages/core/src/api/blockManipulation/containers/containers.browser.test.ts
new file mode 100644
index 0000000000..c8ba730811
--- /dev/null
+++ b/packages/core/src/api/blockManipulation/containers/containers.browser.test.ts
@@ -0,0 +1,279 @@
+import {
+  afterAll,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+} from "vite-plus/test";
+import { userEvent } from "vite-plus/test/browser";
+
+import { BlockNoteEditor } from "../../../editor/BlockNoteEditor.js";
+import { containerSchema } from "./containers.fixture.js";
+
+// The halves of the container-block story that need a real browser, split off
+// from the (node) `containers.test.ts`:
+//
+//  - the keymap, which tiptap can only reach through a mounted view. These used
+//    to synthesize a `KeyboardEvent` and hand it to `handleKeyDown` directly,
+//    which passes whether or not a real keypress ever gets there. Here the
+//    editor is mounted and focused and the keys are pressed for real.
+//  - HTML/markdown serialization, which builds and parses real DOM.
+
+const schema = containerSchema;
+
+let editor: BlockNoteEditor<
+  typeof schema.blockSchema,
+  typeof schema.inlineContentSchema,
+  typeof schema.styleSchema
+>;
+let div: HTMLElement;
+
+beforeAll(() => {
+  div = document.createElement("div");
+  document.body.appendChild(div);
+  editor = BlockNoteEditor.create({ schema });
+  editor.mount(div);
+});
+
+afterAll(() => {
+  editor._tiptapEditor.destroy();
+  div.remove();
+  editor = undefined as any;
+});
+
+beforeEach(() => {
+  editor.replaceBlocks(editor.document, [
+    { id: "p-0", type: "paragraph", content: "Paragraph 0" },
+    { id: "p-1", type: "paragraph", content: "Paragraph 1" },
+  ]);
+});
+
+/** Puts the caret where the test wants it and presses the key for real. */
+async function pressKey(
+  key: string,
+  at: { block: string; placement: "start" | "end" },
+) {
+  editor.setTextCursorPosition(at.block, at.placement);
+  editor.focus();
+  await userEvent.keyboard(`{${key}}`);
+}
+
+describe("children keyboard handling", () => {
+  it("Enter on an empty last child escapes the container", async () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "callout",
+        id: "c-0",
+        children: [
+          { id: "c-p-0", type: "paragraph", content: "Hello" },
+          { id: "c-p-1", type: "paragraph", content: "" },
+        ],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    await pressKey("Enter", { block: "c-p-1", placement: "end" });
+
+    // The empty block has moved out of the callout, becoming its next sibling.
+    const callout = editor.getBlock("c-0")!;
+    expect(callout.children.map((child) => child.id)).toEqual(["c-p-0"]);
+    expect(editor.document.map((block) => block.type)).toEqual([
+      "callout",
+      "paragraph",
+      "paragraph",
+    ]);
+    expect(editor.document.map((block) => block.id)).toEqual([
+      "c-0",
+      "c-p-1",
+      "trailing",
+    ]);
+    // The caret came with it, so typing continues outside the container.
+    expect(editor.getTextCursorPosition().block.id).toBe("c-p-1");
+  });
+
+  it("Enter does not escape a container with exitOnEnter: false", async () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "lockedBox",
+        id: "l-0",
+        children: [
+          { id: "l-p-0", type: "paragraph", content: "Hello" },
+          { id: "l-p-1", type: "paragraph", content: "" },
+        ],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    await pressKey("Enter", { block: "l-p-1", placement: "end" });
+
+    // Still exactly one top-level lockedBox followed by the trailing
+    // paragraph; the new block was created *inside* the container. Asserted as
+    // a change (2 children -> 3) rather than as "nothing moved out", so the
+    // test can't pass by the keypress never arriving at all.
+    expect(editor.document.map((block) => block.type)).toEqual([
+      "lockedBox",
+      "paragraph",
+    ]);
+    const children = editor.getBlock("l-0")!.children;
+    expect(children.map((child) => child.id).slice(0, 2)).toEqual([
+      "l-p-0",
+      "l-p-1",
+    ]);
+    expect(children).toHaveLength(3);
+    expect(editor.getTextCursorPosition().block.id).toBe(children[2].id);
+  });
+
+  it("Backspace at the start of a container's first child moves it out", async () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "before", type: "paragraph", content: "Before" },
+      {
+        type: "callout",
+        id: "c-0",
+        children: [
+          { id: "c-p-0", type: "paragraph", content: "First" },
+          { id: "c-p-1", type: "paragraph", content: "Second" },
+        ],
+      },
+    ]);
+
+    await pressKey("Backspace", { block: "c-p-0", placement: "start" });
+
+    // The first child has moved out, above the callout, with its text intact.
+    expect(editor.getBlock("c-0")!.children.map((child) => child.id)).toEqual([
+      "c-p-1",
+    ]);
+    expect(editor.document.map((block) => block.id)).toEqual([
+      "before",
+      "c-p-0",
+      "c-0",
+    ]);
+    expect(editor.getBlock("c-p-0")!.content).toEqual([
+      { type: "text", text: "First", styles: {} },
+    ]);
+  });
+
+  it("Backspace at the start of a block after a container moves it inside", async () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "callout",
+        id: "c-0",
+        children: [{ id: "c-p-0", type: "paragraph", content: "In callout" }],
+      },
+      { id: "after", type: "paragraph", content: "After" },
+    ]);
+
+    await pressKey("Backspace", { block: "after", placement: "start" });
+
+    expect(editor.getBlock("c-0")!.children.map((child) => child.id)).toEqual([
+      "c-p-0",
+      "after",
+    ]);
+    expect(editor.document.map((block) => block.id)).toEqual(["c-0"]);
+    expect(editor.getBlock("after")!.content).toEqual([
+      { type: "text", text: "After", styles: {} },
+    ]);
+  });
+
+  it("Delete at the end of a block before a container pulls its first child out", async () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "before", type: "paragraph", content: "Before" },
+      {
+        type: "callout",
+        id: "c-0",
+        children: [
+          { id: "c-p-0", type: "paragraph", content: "First" },
+          { id: "c-p-1", type: "paragraph", content: "Second" },
+        ],
+      },
+    ]);
+
+    await pressKey("Delete", { block: "before", placement: "end" });
+
+    expect(editor.document.map((block) => block.id)).toEqual([
+      "before",
+      "c-p-0",
+      "c-0",
+    ]);
+    expect(editor.getBlock("c-0")!.children.map((child) => child.id)).toEqual([
+      "c-p-1",
+    ]);
+  });
+
+  it("Delete at the end of a container's last child pulls the next block in", async () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "callout",
+        id: "c-0",
+        children: [{ id: "c-p-0", type: "paragraph", content: "In callout" }],
+      },
+      { id: "after", type: "paragraph", content: "After" },
+    ]);
+
+    await pressKey("Delete", { block: "c-p-0", placement: "end" });
+
+    expect(editor.getBlock("c-0")!.children.map((child) => child.id)).toEqual([
+      "c-p-0",
+      "after",
+    ]);
+    expect(editor.document.map((block) => block.id)).toEqual(["c-0"]);
+  });
+});
+
+describe("children conversion", () => {
+  it("round-trips a container through full (internal) HTML", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "callout" as const,
+        id: "c-0",
+        props: { flavor: "warning" as const },
+        children: [
+          { id: "c-p-0", type: "paragraph" as const, content: "In callout" },
+        ],
+      },
+    ]);
+
+    const html = editor.blocksToFullHTML(editor.document);
+    expect(html).toContain('data-node-type="callout"');
+
+    const parsed = editor.tryParseHTMLToBlocks(html);
+    expect(parsed[0].type).toBe("callout");
+    expect((parsed[0].props as any).flavor).toBe("warning");
+    expect(parsed[0].children).toHaveLength(1);
+    expect(parsed[0].children[0].type).toBe("paragraph");
+  });
+
+  it("exports containers to external HTML with type + prop attributes", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "callout",
+        id: "c-0",
+        props: { flavor: "warning" },
+        children: [{ id: "c-p-0", type: "paragraph", content: "In callout" }],
+      },
+    ]);
+
+    const html = editor.blocksToHTMLLossy(editor.document);
+    expect(html).toContain('data-node-type="callout"');
+    expect(html).toContain('data-flavor="warning"');
+    // Container output is not wrapped in a blockContent div.
+    expect(html).not.toContain("bn-block-content");
+  });
+
+  it("flattens containers to their children in markdown export", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "callout",
+        id: "c-0",
+        children: [
+          { id: "c-p-0", type: "paragraph", content: "In callout" },
+          { id: "c-p-1", type: "heading", content: "Heading in callout" },
+        ],
+      },
+    ]);
+
+    const markdown = editor.blocksToMarkdownLossy(editor.document);
+    expect(markdown).toContain("In callout");
+    expect(markdown).toContain("# Heading in callout");
+  });
+});
diff --git a/packages/core/src/api/blockManipulation/containers/containers.fixture.ts b/packages/core/src/api/blockManipulation/containers/containers.fixture.ts
new file mode 100644
index 0000000000..e6ba95f584
--- /dev/null
+++ b/packages/core/src/api/blockManipulation/containers/containers.fixture.ts
@@ -0,0 +1,71 @@
+import { BlockNoteSchema } from "../../../blocks/BlockNoteSchema.js";
+import { defaultBlockSpecs } from "../../../blocks/defaultBlocks.js";
+import { createBlockSpec } from "../../../schema/blocks/createSpec.js";
+
+const renderDiv = () => {
+  const dom = document.createElement("div");
+  return { dom, contentDOM: dom };
+};
+
+const Callout = createBlockSpec(
+  {
+    type: "callout" as const,
+    propSchema: {
+      flavor: {
+        default: "tip",
+        values: ["tip", "info", "warning", "success"],
+      },
+    },
+    content: "none",
+    children: {
+      min: 1,
+      default: [{ type: "paragraph" }],
+    },
+  },
+  { render: renderDiv },
+)();
+
+const LockedBox = createBlockSpec(
+  {
+    type: "lockedBox" as const,
+    propSchema: {},
+    content: "none",
+    children: { min: 1, exitOnEnter: false },
+  },
+  { render: renderDiv },
+)();
+
+const Grid = createBlockSpec(
+  {
+    type: "grid" as const,
+    propSchema: {},
+    content: "none",
+    children: {
+      allow: { blocks: false, containers: ["gridCell"] },
+      min: 2,
+      unwrapWhenEmptied: true,
+    },
+  },
+  { render: renderDiv },
+)();
+
+const GridCell = createBlockSpec(
+  {
+    type: "gridCell" as const,
+    propSchema: {},
+    content: "none",
+    children: {},
+    placement: "containerOnly",
+  },
+  { render: renderDiv },
+)();
+
+export const containerSchema = BlockNoteSchema.create().extend({
+  blockSpecs: {
+    ...defaultBlockSpecs,
+    callout: Callout,
+    lockedBox: LockedBox,
+    grid: Grid,
+    gridCell: GridCell,
+  } as const,
+});
diff --git a/packages/core/src/api/blockManipulation/containers/containers.test.ts b/packages/core/src/api/blockManipulation/containers/containers.test.ts
new file mode 100644
index 0000000000..747e6325a3
--- /dev/null
+++ b/packages/core/src/api/blockManipulation/containers/containers.test.ts
@@ -0,0 +1,355 @@
+// @vitest-environment node
+import {
+  afterAll,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+} from "vite-plus/test";
+
+import { BlockNoteEditor } from "../../../editor/BlockNoteEditor.js";
+import { containerSchema } from "./containers.fixture.js";
+
+type PartialBlock = (typeof containerSchema)["PartialBlock"];
+
+// Document-model behaviour of container blocks: seeding, schema enforcement,
+// repair and selection. All of it is `Block` JSON in and `Block` JSON out, so
+// the editor stays headless and this suite runs with no DOM at all.
+//
+// The halves that genuinely need one — the keymap (which tiptap can only reach
+// through a mounted view) and HTML/markdown serialization (which builds real
+// DOM) — live in `containers.browser.test.ts`.
+
+const schema = containerSchema;
+
+let editor: BlockNoteEditor<
+  typeof schema.blockSchema,
+  typeof schema.inlineContentSchema,
+  typeof schema.styleSchema
+>;
+
+beforeAll(() => {
+  editor = BlockNoteEditor.create({ schema });
+});
+
+afterAll(() => {
+  editor._tiptapEditor.destroy();
+  editor = undefined as any;
+});
+
+beforeEach(() => {
+  editor.replaceBlocks(editor.document, [
+    { id: "p-0", type: "paragraph", content: "Paragraph 0" },
+    { id: "p-1", type: "paragraph", content: "Paragraph 1" },
+  ]);
+});
+
+describe("children insertion & seeding", () => {
+  it("seeds `default` when inserted without children", () => {
+    editor.insertBlocks([{ type: "callout", id: "c-0" }], "p-1", "after");
+
+    const callout = editor.getBlock("c-0")!;
+    expect(callout.children).toHaveLength(1);
+    expect(callout.children[0].type).toBe("paragraph");
+  });
+
+  // The minimal container config used to be a landmine: `min` defaults to 1,
+  // nothing seeded it, and the most obvious insert threw a raw ProseMirror
+  // `RangeError: Invalid content for node ...`.
+  it("fills a container that has no `default` rather than throwing", () => {
+    expect(() =>
+      editor.insertBlocks([{ type: "lockedBox", id: "b-0" }], "p-1", "after"),
+    ).not.toThrow();
+
+    const box = editor.getBlock("b-0")!;
+    expect(box.children).toHaveLength(1);
+    expect(box.children[0].type).toBe("paragraph");
+  });
+
+  it("gives auto-filled children real ids", () => {
+    // Auto-filled nodes come straight from the schema with `id: null`, and the
+    // UniqueID plugin never sees them — `insertBlocks` converts back through
+    // `nodeToBlock` before the transaction is dispatched.
+    editor.insertBlocks([{ type: "lockedBox", id: "b-0" }], "p-1", "after");
+
+    const child = editor.getBlock("b-0")!.children[0];
+    expect(child.id).toBeTruthy();
+    expect(editor.getBlock(child.id)).toBeDefined();
+  });
+
+  it("does not re-seed a container round-tripped through the document", () => {
+    editor.insertBlocks([{ type: "callout", id: "c-0" }], "p-1", "after");
+    const inserted = editor.getBlock("c-0")!;
+
+    // `nodeToBlock` always emits an array, so a round-trip must not read an
+    // empty one as "unspecified" and seed on top of it.
+    editor.replaceBlocks([inserted], [inserted]);
+
+    expect(editor.getBlock("c-0")!.children).toHaveLength(
+      inserted.children.length,
+    );
+  });
+
+  // `children: []` is a caller asking for a container with no children, which
+  // a `min: 1` container cannot be. It used to be taken at face value, which
+  // built a node below its minimum: `insertBlocks` then threw a raw
+  // `Invalid content for node callout: <>` from its `node.check()`.
+  it("fills an explicitly empty `children` array up to `min`", () => {
+    expect(() =>
+      editor.insertBlocks(
+        [{ type: "callout", id: "c-0", children: [] }],
+        "p-1",
+        "after",
+      ),
+    ).not.toThrow();
+
+    const callout = editor.getBlock("c-0")!;
+    expect(callout.children).toHaveLength(1);
+    expect(callout.children[0].type).toBe("paragraph");
+    expect(callout.children[0].id).toBeTruthy();
+  });
+
+  it("does not pad explicit children that already satisfy the config", () => {
+    editor.insertBlocks(
+      [
+        {
+          type: "grid",
+          id: "g-0",
+          children: [{ type: "gridCell" }, { type: "gridCell" }],
+        },
+      ],
+      "p-1",
+      "after",
+    );
+
+    expect(editor.getBlock("g-0")!.children).toHaveLength(2);
+  });
+
+  // A container that unwraps as it empties out is the one case explicit
+  // children are *not* padded: adding a second column to a one-column
+  // columnList would invent content the next repair pass deletes anyway.
+  it("refuses rather than pads a container that unwraps when emptied", () => {
+    expect(() =>
+      editor.insertBlocks(
+        [{ type: "grid", id: "g-1", children: [{ type: "gridCell" }] }],
+        "p-1",
+        "after",
+      ),
+    ).toThrow();
+  });
+
+  // A pure container has no content of its own, but the block it replaces did
+  // — so that content becomes its first child rather than being dropped.
+  it("carries content into the first child when converting via updateBlock", () => {
+    editor.updateBlock("p-1", { type: "callout" });
+
+    const callout = editor.document[1];
+    expect(callout.type).toBe("callout");
+    expect(callout.children).toHaveLength(1);
+    expect(callout.children[0].type).toBe("paragraph");
+    expect(callout.children[0].content).toEqual([
+      { type: "text", text: "Paragraph 1", styles: {} },
+    ]);
+  });
+
+  it("seeds `default` when converting an empty block via updateBlock", () => {
+    editor.updateBlock("p-1", { content: [] });
+    editor.updateBlock("p-1", { type: "callout" });
+
+    const callout = editor.document[1];
+    expect(callout.type).toBe("callout");
+    expect(callout.children).toHaveLength(1);
+    expect(callout.children[0].type).toBe("paragraph");
+    expect(callout.children[0].content).toEqual([]);
+  });
+
+  it("accepts arbitrary block children, including nested containers", () => {
+    editor.insertBlocks(
+      [
+        {
+          type: "callout",
+          id: "c-0",
+          children: [
+            { type: "heading", content: "In callout" },
+            {
+              type: "callout",
+              id: "c-1",
+              children: [{ type: "paragraph", content: "Nested" }],
+            },
+          ],
+        },
+      ],
+      "p-1",
+      "after",
+    );
+
+    const callout = editor.getBlock("c-0")!;
+    expect(callout.children.map((child) => child.type)).toEqual([
+      "heading",
+      "callout",
+    ]);
+    expect(editor.getBlock("c-1")!.children[0].type).toBe("paragraph");
+  });
+
+  it("rejects non-allowed children for a restricted container", () => {
+    expect(() =>
+      editor.insertBlocks(
+        [
+          {
+            type: "grid",
+            children: [
+              { type: "paragraph", content: "not a cell" },
+              { type: "paragraph", content: "not a cell" },
+            ],
+          },
+        ],
+        "p-1",
+        "after",
+      ),
+    ).toThrow();
+  });
+
+  it("accepts allowed children for a restricted container", () => {
+    editor.insertBlocks(
+      [
+        {
+          type: "grid",
+          id: "g-0",
+          children: [
+            {
+              type: "gridCell",
+              children: [{ type: "paragraph", content: "Cell A" }],
+            },
+            {
+              type: "gridCell",
+              children: [{ type: "paragraph", content: "Cell B" }],
+            },
+          ],
+        },
+      ],
+      "p-1",
+      "after",
+    );
+
+    const grid = editor.getBlock("g-0")!;
+    expect(grid.children.map((child) => child.type)).toEqual([
+      "gridCell",
+      "gridCell",
+    ]);
+  });
+
+  it("rejects inserting a containerOnly block at the document root", () => {
+    expect(() =>
+      editor.insertBlocks(
+        [{ type: "gridCell", children: [{ type: "paragraph" }] }],
+        "p-1",
+        "after",
+      ),
+    ).toThrow();
+  });
+});
+
+// `initialContent` is the only path that builds a document without validating
+// it: `blockToNode` is deliberately lenient, and `createDocument` builds from
+// JSON. So blocks `insertBlocks` rejects used to load happily, and a container
+// below its `min` stayed below it for the life of the document.
+describe("initialContent enforcement", () => {
+  const createWith = (initialContent: PartialBlock[]) => {
+    return BlockNoteEditor.create({ schema, initialContent });
+  };
+
+  it("fills an explicitly empty `children` array up to `min`", () => {
+    const loaded = createWith([{ type: "callout", id: "c-0", children: [] }]);
+
+    const callout = loaded.getBlock("c-0")!;
+    expect(callout.children).toHaveLength(1);
+    expect(callout.children[0].type).toBe("paragraph");
+
+    loaded._tiptapEditor.destroy();
+  });
+
+  it("rejects a container it cannot legally fill", () => {
+    expect(() =>
+      createWith([
+        { type: "grid", id: "g-0", children: [{ type: "gridCell" }] },
+      ]),
+    ).toThrow(/initialContent/);
+  });
+});
+
+describe("children repair", () => {
+  it("keeps a default container when its only child is removed (refilled)", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "callout",
+        id: "c-0",
+        children: [{ id: "c-p-0", type: "paragraph", content: "Only child" }],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    editor.removeBlocks(["c-p-0"]);
+
+    const callout = editor.getBlock("c-0")!;
+    expect(callout).toBeDefined();
+    expect(callout.children).toHaveLength(1);
+    expect(callout.children[0].type).toBe("paragraph");
+    expect(callout.children[0].content).toEqual([]);
+  });
+
+  it("unwraps a repair-configured container when only one non-empty child remains", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "grid",
+        id: "g-0",
+        children: [
+          {
+            type: "gridCell",
+            id: "cell-a",
+            children: [{ id: "cell-a-p", type: "paragraph", content: "A" }],
+          },
+          {
+            type: "gridCell",
+            id: "cell-b",
+            children: [{ id: "cell-b-p", type: "paragraph", content: "B" }],
+          },
+        ],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    editor.removeBlocks(["cell-a-p"]);
+
+    expect(editor.document).toMatchSnapshot();
+    // The grid has been unwrapped: cell B's content replaced it.
+    expect(editor.getBlock("g-0")).toBeUndefined();
+    expect(editor.document.map((block) => block.id)).toEqual([
+      "cell-b-p",
+      "trailing",
+    ]);
+  });
+});
+
+describe("children selection", () => {
+  it("getSelectionCutBlocks handles selections reaching into a container", () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "before", type: "paragraph", content: "Before" },
+      {
+        type: "callout",
+        id: "c-0",
+        children: [
+          { id: "c-p-0", type: "paragraph", content: "First" },
+          { id: "c-p-1", type: "paragraph", content: "Second" },
+        ],
+      },
+    ]);
+    editor.setSelection("before", "c-p-0");
+
+    // Previously threw "unexpected" for any partial selection touching a
+    // container (breaking comments/AI selection handling).
+    const result = editor.getSelectionCutBlocks();
+    expect(result.blocks.length).toBeGreaterThanOrEqual(1);
+    expect(result.blocks.map((block) => block.id)).toContain("before");
+  });
+});
diff --git a/packages/core/src/api/blockManipulation/containers/contentContainers.browser.test.ts b/packages/core/src/api/blockManipulation/containers/contentContainers.browser.test.ts
new file mode 100644
index 0000000000..5ac50d0fab
--- /dev/null
+++ b/packages/core/src/api/blockManipulation/containers/contentContainers.browser.test.ts
@@ -0,0 +1,259 @@
+import {
+  afterAll,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+} from "vite-plus/test";
+import { userEvent } from "vite-plus/test/browser";
+
+import { BlockNoteEditor } from "../../../editor/BlockNoteEditor.js";
+import { contentContainerSchema } from "./contentContainers.fixture.js";
+
+// The keymap half of the content-bearing container story, split off from the
+// (node) `contentContainers.test.ts`. Tiptap can only reach `handleKeyDown`
+// through a mounted view, and these used to synthesize a `KeyboardEvent` and
+// call the handler directly — which passes whether or not a real keypress ever
+// gets there. Here the editor is mounted and focused and the keys are pressed
+// for real.
+//
+// Not ported: "Enter at the end of the title creates a new first child". That
+// exact behaviour, caret included, is already covered against a real app in
+// `tests/src/end-to-end/containerblocks/containerblocks.test.tsx`
+// ("Creates a first child on Enter at the end of a container's content").
+
+const schema = contentContainerSchema;
+
+let editor: BlockNoteEditor<
+  typeof schema.blockSchema,
+  typeof schema.inlineContentSchema,
+  typeof schema.styleSchema
+>;
+let div: HTMLElement;
+
+beforeAll(() => {
+  div = document.createElement("div");
+  document.body.appendChild(div);
+  editor = BlockNoteEditor.create({ schema });
+  editor.mount(div);
+});
+
+afterAll(() => {
+  editor._tiptapEditor.destroy();
+  div.remove();
+  editor = undefined as any;
+});
+
+beforeEach(() => {
+  editor.replaceBlocks(editor.document, [
+    { id: "p-0", type: "paragraph", content: "Paragraph 0" },
+  ]);
+});
+
+/** Puts the caret where the test wants it and presses the key for real. */
+async function pressKey(
+  key: string,
+  at: { block: string; placement: "start" | "end"; offset?: number },
+) {
+  editor.setTextCursorPosition(at.block, at.placement);
+  if (at.offset) {
+    editor._tiptapEditor.commands.setTextSelection(
+      editor._tiptapEditor.state.selection.from + at.offset,
+    );
+  }
+  editor.focus();
+  await userEvent.keyboard(`{${key}}`);
+}
+
+describe("content-bearing container: keyboard", () => {
+  it("Backspace at the start of the title unwraps the container", async () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "before", type: "paragraph", content: "Before" },
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "Title",
+        children: [
+          { id: "t-p-0", type: "paragraph", content: "First" },
+          { id: "t-p-1", type: "paragraph", content: "Second" },
+        ],
+      },
+    ]);
+
+    await pressKey("Backspace", { block: "t-0", placement: "start" });
+
+    // The title became a paragraph's content and the children came along as
+    // that paragraph's children — nothing was destroyed.
+    const unwrapped = editor.document[1];
+    expect(unwrapped.type).toBe("paragraph");
+    expect(unwrapped.content).toEqual([
+      { type: "text", text: "Title", styles: {} },
+    ]);
+    expect(unwrapped.children.map((child) => child.id)).toEqual([
+      "t-p-0",
+      "t-p-1",
+    ]);
+  });
+
+  it("Backspace at the start of the first child merges it into the title", async () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "Title",
+        children: [
+          { id: "t-p-0", type: "paragraph", content: "First" },
+          { id: "t-p-1", type: "paragraph", content: "Second" },
+        ],
+      },
+    ]);
+
+    await pressKey("Backspace", { block: "t-p-0", placement: "start" });
+
+    const toggle = editor.getBlock("t-0")!;
+    expect(toggle.content).toEqual([
+      { type: "text", text: "TitleFirst", styles: {} },
+    ]);
+    expect(toggle.children.map((child) => child.id)).toEqual(["t-p-1"]);
+  });
+
+  it("Backspace at the start of a pure container's first child still moves it out", async () => {
+    // The control for the two cases above: a container with no title of its own
+    // must keep the old behaviour.
+    editor.replaceBlocks(editor.document, [
+      { id: "before", type: "paragraph", content: "Before" },
+      {
+        type: "callout",
+        id: "c-0",
+        children: [
+          { id: "c-p-0", type: "paragraph", content: "First" },
+          { id: "c-p-1", type: "paragraph", content: "Second" },
+        ],
+      },
+    ]);
+
+    await pressKey("Backspace", { block: "c-p-0", placement: "start" });
+
+    expect(editor.getBlock("c-0")!.children.map((child) => child.id)).toEqual([
+      "c-p-1",
+    ]);
+    expect(editor.document.map((block) => block.id)[1]).toBe("c-p-0");
+  });
+
+  it("Enter mid-title splits, with the tail becoming the first child", async () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "TitleTail",
+        children: [{ id: "t-p-0", type: "paragraph", content: "First" }],
+      },
+    ]);
+
+    await pressKey("Enter", { block: "t-0", placement: "start", offset: 5 });
+
+    const toggle = editor.getBlock("t-0")!;
+    expect(toggle.content).toEqual([
+      { type: "text", text: "Title", styles: {} },
+    ]);
+    expect(toggle.children[0].content).toEqual([
+      { type: "text", text: "Tail", styles: {} },
+    ]);
+    expect(toggle.children[1].id).toBe("t-p-0");
+  });
+
+  it("Enter on an empty last child still escapes the container", async () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "Title",
+        children: [
+          { id: "t-p-0", type: "paragraph", content: "First" },
+          { id: "t-p-1", type: "paragraph", content: "" },
+        ],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    await pressKey("Enter", { block: "t-p-1", placement: "end" });
+
+    expect(editor.getBlock("t-0")!.children.map((child) => child.id)).toEqual([
+      "t-p-0",
+    ]);
+    expect(editor.document.map((block) => block.id)).toEqual([
+      "t-0",
+      "t-p-1",
+      "trailing",
+    ]);
+    // The container kept its own title through the escape.
+    expect(editor.getBlock("t-0")!.content).toEqual([
+      { type: "text", text: "Title", styles: {} },
+    ]);
+  });
+
+  it("Delete at the end of the title pulls the first child's content up", async () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "Title",
+        children: [
+          { id: "t-p-0", type: "paragraph", content: "First" },
+          { id: "t-p-1", type: "paragraph", content: "Second" },
+        ],
+      },
+    ]);
+
+    await pressKey("Delete", { block: "t-0", placement: "end" });
+
+    const toggle = editor.getBlock("t-0")!;
+    expect(toggle.content).toEqual([
+      { type: "text", text: "TitleFirst", styles: {} },
+    ]);
+    expect(toggle.children.map((child) => child.id)).toEqual(["t-p-1"]);
+  });
+
+  it("Delete at the end of the title of a container that must keep a child", async () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "Title",
+        children: [{ id: "t-p-0", type: "paragraph", content: "Only" }],
+      },
+    ]);
+
+    await pressKey("Delete", { block: "t-0", placement: "end" });
+
+    const toggle = editor.getBlock("t-0")!;
+    expect(toggle.content).toEqual([
+      { type: "text", text: "TitleOnly", styles: {} },
+    ]);
+    // `min: 1` — the schema refills the emptied children node.
+    expect(toggle.children).toHaveLength(1);
+    expect(toggle.children[0].content).toEqual([]);
+  });
+
+  it("Delete in a childless container does not throw", async () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "optionalToggle",
+        id: "t-0",
+        content: "Title",
+        children: [],
+      },
+      { id: "after", type: "paragraph", content: "After" },
+    ]);
+
+    await pressKey("Delete", { block: "t-0", placement: "end" });
+
+    // Delete at the end of a childless container's title reaches past it to the
+    // next block. What matters is that it doesn't throw; asserted as a real
+    // change so the test can't pass by the keypress never arriving.
+    expect(editor.getBlock("t-0")!.content).toEqual([
+      { type: "text", text: "TitleAfter", styles: {} },
+    ]);
+  });
+});
diff --git a/packages/core/src/api/blockManipulation/containers/contentContainers.fixture.ts b/packages/core/src/api/blockManipulation/containers/contentContainers.fixture.ts
new file mode 100644
index 0000000000..cac5500d73
--- /dev/null
+++ b/packages/core/src/api/blockManipulation/containers/contentContainers.fixture.ts
@@ -0,0 +1,94 @@
+import { BlockNoteSchema } from "../../../blocks/BlockNoteSchema.js";
+import { defaultBlockSpecs } from "../../../blocks/defaultBlocks.js";
+import { createBlockSpec } from "../../../schema/blocks/createSpec.js";
+
+// The content-bearing container schema shared by `contentContainers.test.ts`
+// (node: document model) and `contentContainers.browser.test.ts` (real browser:
+// keymap), so both halves are describing the same blocks.
+
+const renderDiv = () => {
+  const dom = document.createElement("div");
+  return { dom, contentDOM: dom };
+};
+
+// The toggle shape: a container with its own inline content (its "title") as
+// well as children. `min: 1`, so it always keeps at least one child.
+const Toggle = createBlockSpec(
+  {
+    type: "toggle" as const,
+    propSchema: { open: { default: true } },
+    content: "inline",
+    children: {},
+  },
+  { render: renderDiv },
+)();
+
+// The same, but allowed to hold no children at all — the `min: 0` shape that
+// has no addressable child to fall back on.
+const OptionalToggle = createBlockSpec(
+  {
+    type: "optionalToggle" as const,
+    propSchema: {},
+    content: "inline",
+    children: { min: 0 },
+  },
+  { render: renderDiv },
+)();
+
+// A content-bearing container that unwraps as it empties out, paired with the
+// pure container below. Repair has to treat these two identically apart from
+// the title.
+const TitledGrid = createBlockSpec(
+  {
+    type: "titledGrid" as const,
+    propSchema: {},
+    content: "inline",
+    children: { min: 2, unwrapWhenEmptied: true },
+  },
+  { render: renderDiv },
+)();
+
+const PureGrid = createBlockSpec(
+  {
+    type: "pureGrid" as const,
+    propSchema: {},
+    content: "none",
+    children: { min: 2, unwrapWhenEmptied: true },
+  },
+  { render: renderDiv },
+)();
+
+// A pure container, for the "never regress" half of every pair.
+const Callout = createBlockSpec(
+  {
+    type: "callout" as const,
+    propSchema: {},
+    content: "none",
+    children: { min: 1, default: [{ type: "paragraph" }] },
+  },
+  { render: renderDiv },
+)();
+
+// A pure container allowed to hold nothing — the shape that has no child to
+// place a text cursor in.
+const EmptyBox = createBlockSpec(
+  {
+    type: "emptyBox" as const,
+    propSchema: {},
+    content: "none",
+    children: { min: 0 },
+  },
+  { render: renderDiv },
+)();
+
+export const contentContainerSchema = BlockNoteSchema.create().extend({
+  blockSpecs: {
+    ...defaultBlockSpecs,
+    toggle: Toggle,
+    optionalToggle: OptionalToggle,
+    titledGrid: TitledGrid,
+    pureGrid: PureGrid,
+    callout: Callout,
+    emptyBox: EmptyBox,
+  } as const,
+});
diff --git a/packages/core/src/api/blockManipulation/containers/contentContainers.test.ts b/packages/core/src/api/blockManipulation/containers/contentContainers.test.ts
new file mode 100644
index 0000000000..0b423bc10b
--- /dev/null
+++ b/packages/core/src/api/blockManipulation/containers/contentContainers.test.ts
@@ -0,0 +1,358 @@
+// @vitest-environment node
+import {
+  afterAll,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+} from "vite-plus/test";
+
+import { BlockNoteEditor } from "../../../editor/BlockNoteEditor.js";
+import { contentContainerSchema } from "./contentContainers.fixture.js";
+
+// Document-model behaviour of content-bearing containers (the "toggle" shape:
+// a container with its own inline content as well as children): repair,
+// childless handling, `updateBlock` and selection. All `Block` JSON in and
+// `Block` JSON out, so the editor stays headless and this suite needs no DOM.
+//
+// The keymap half lives in `contentContainers.browser.test.ts`: tiptap can only
+// reach `handleKeyDown` through a mounted view.
+
+const schema = contentContainerSchema;
+
+let editor: BlockNoteEditor<
+  typeof schema.blockSchema,
+  typeof schema.inlineContentSchema,
+  typeof schema.styleSchema
+>;
+
+beforeAll(() => {
+  editor = BlockNoteEditor.create({ schema });
+});
+
+afterAll(() => {
+  editor._tiptapEditor.destroy();
+  editor = undefined as any;
+});
+
+beforeEach(() => {
+  editor.replaceBlocks(editor.document, [
+    { id: "p-0", type: "paragraph", content: "Paragraph 0" },
+  ]);
+});
+
+describe("content-bearing container: repair", () => {
+  // The whole point of the title is that it holds text the user typed.
+  // Unwrapping the container throws its node — and therefore its title — away,
+  // so repair must refuse rather than silently destroy it.
+  it("does not unwrap a container whose title has content", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "titledGrid",
+        id: "g-0",
+        content: "Kept title",
+        children: [
+          { id: "g-p-0", type: "paragraph", content: "A" },
+          { id: "g-p-1", type: "paragraph", content: "B" },
+        ],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    editor.removeBlocks(["g-p-0"]);
+
+    const grid = editor.getBlock("g-0");
+    expect(grid).toBeDefined();
+    expect(grid!.content).toEqual([
+      { type: "text", text: "Kept title", styles: {} },
+    ]);
+    // `min: 2`, so ProseMirror refills the removed child rather than letting
+    // the container drop below what its content expression requires.
+    expect(grid!.children).toHaveLength(2);
+    expect(grid!.children.map((child) => child.id)).toContain("g-p-1");
+  });
+
+  it("unwraps a container whose title is empty", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "titledGrid",
+        id: "g-0",
+        content: "",
+        children: [
+          { id: "g-p-0", type: "paragraph", content: "A" },
+          { id: "g-p-1", type: "paragraph", content: "B" },
+        ],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    editor.removeBlocks(["g-p-0"]);
+
+    expect(editor.getBlock("g-0")).toBeUndefined();
+    expect(editor.document.map((block) => block.id)).toEqual([
+      "g-p-1",
+      "trailing",
+    ]);
+  });
+
+  it("unwraps the equivalent pure container the same way", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "pureGrid",
+        id: "g-0",
+        children: [
+          { id: "g-p-0", type: "paragraph", content: "A" },
+          { id: "g-p-1", type: "paragraph", content: "B" },
+        ],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    editor.removeBlocks(["g-p-0"]);
+
+    expect(editor.getBlock("g-0")).toBeUndefined();
+    expect(editor.document.map((block) => block.id)).toEqual([
+      "g-p-1",
+      "trailing",
+    ]);
+  });
+
+  it("deletes a titleless container that empties out completely", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "titledGrid",
+        id: "g-0",
+        content: "",
+        children: [
+          { id: "g-p-0", type: "paragraph", content: "A" },
+          { id: "g-p-1", type: "paragraph", content: "B" },
+        ],
+      },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+
+    editor.removeBlocks(["g-p-0", "g-p-1"]);
+
+    expect(editor.getBlock("g-0")).toBeUndefined();
+    expect(editor.document.map((block) => block.id)).toEqual(["trailing"]);
+  });
+});
+
+describe("content-bearing container: childless container", () => {
+  it("setTextCursorPosition on a childless pure container does not throw", () => {
+    // A pure container that allows zero children has no child to descend into.
+    editor.replaceBlocks(editor.document, [
+      { id: "p-0", type: "paragraph", content: "Paragraph 0" },
+    ]);
+    editor.insertBlocks(
+      [{ type: "emptyBox", id: "b-0", children: [] } as any],
+      "p-0",
+      "after",
+    );
+
+    expect(() => editor.setTextCursorPosition("b-0", "start")).not.toThrow();
+    expect(() => editor.setTextCursorPosition("b-0", "end")).not.toThrow();
+  });
+
+  it("setTextCursorPosition on a childless content-bearing container works", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "optionalToggle",
+        id: "t-0",
+        content: "Title",
+        children: [],
+      },
+    ]);
+
+    editor.setTextCursorPosition("t-0", "end");
+    expect(editor.getTextCursorPosition().block.id).toBe("t-0");
+  });
+});
+
+describe("content-bearing container: updateBlock", () => {
+  it("updates the title in place", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "Title",
+        children: [{ id: "t-p-0", type: "paragraph", content: "Child" }],
+      },
+    ]);
+
+    editor.updateBlock("t-0", { content: "New title" });
+
+    const toggle = editor.getBlock("t-0")!;
+    expect(toggle.content).toEqual([
+      { type: "text", text: "New title", styles: {} },
+    ]);
+    // Children (and their ids) are untouched.
+    expect(toggle.children.map((child) => child.id)).toEqual(["t-p-0"]);
+  });
+
+  it("updates props without touching content or children", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "Title",
+        children: [{ id: "t-p-0", type: "paragraph", content: "Child" }],
+      },
+    ]);
+
+    editor.updateBlock("t-0", { props: { open: false } });
+
+    const toggle = editor.getBlock("t-0")!;
+    expect((toggle.props as any).open).toBe(false);
+    expect(toggle.content).toEqual([
+      { type: "text", text: "Title", styles: {} },
+    ]);
+    expect(toggle.children.map((child) => child.id)).toEqual(["t-p-0"]);
+  });
+
+  it("carries content and children from a paragraph into a container", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        id: "p-0",
+        type: "paragraph",
+        content: "Title",
+        children: [{ id: "p-c-0", type: "paragraph", content: "Child" }],
+      },
+    ]);
+
+    editor.updateBlock("p-0", { type: "toggle" });
+
+    // The full-replace path builds a fresh node, so the block is addressed by
+    // position rather than by id here.
+    const toggle = editor.document[0];
+    expect(toggle.type).toBe("toggle");
+    expect(toggle.content).toEqual([
+      { type: "text", text: "Title", styles: {} },
+    ]);
+    expect(toggle.children.map((child) => child.id)).toEqual(["p-c-0"]);
+  });
+
+  it("carries content and children from a container back to a paragraph", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "Title",
+        children: [{ id: "t-p-0", type: "paragraph", content: "Child" }],
+      },
+    ]);
+
+    editor.updateBlock("t-0", { type: "paragraph" });
+
+    const paragraph = editor.document[0];
+    expect(paragraph.type).toBe("paragraph");
+    expect(paragraph.content).toEqual([
+      { type: "text", text: "Title", styles: {} },
+    ]);
+    expect(paragraph.children.map((child) => child.id)).toEqual(["t-p-0"]);
+  });
+
+  it("carries content into a pure container's first child", () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "p-0", type: "paragraph", content: "Some text" },
+    ]);
+
+    editor.updateBlock("p-0", { type: "callout" });
+
+    const callout = editor.document[0];
+    expect(callout.type).toBe("callout");
+    expect(callout.children).toHaveLength(1);
+    expect(callout.children[0].content).toEqual([
+      { type: "text", text: "Some text", styles: {} },
+    ]);
+  });
+
+  it("drops content that has nowhere to go", () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "p-0", type: "paragraph", content: "Some text" },
+    ]);
+
+    editor.updateBlock("p-0", { type: "image" });
+
+    expect(editor.document[0].type).toBe("image");
+  });
+
+  it("an explicit `content` in the update wins over the carried one", () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "p-0", type: "paragraph", content: "Old" },
+    ]);
+
+    editor.updateBlock("p-0", { type: "toggle", content: "New" });
+
+    expect(editor.document[0].content).toEqual([
+      { type: "text", text: "New", styles: {} },
+    ]);
+  });
+
+  it("treats `children: []` as inert, not as a clear", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "Title",
+        children: [{ id: "t-p-0", type: "paragraph", content: "Child" }],
+      },
+    ]);
+
+    editor.updateBlock("t-0", { children: [], props: { open: false } });
+
+    const toggle = editor.getBlock("t-0")!;
+    expect((toggle.props as any).open).toBe(false);
+    expect(toggle.children.map((child) => child.id)).toEqual(["t-p-0"]);
+  });
+});
+
+describe("content-bearing container: selection", () => {
+  it("getSelectionCutBlocks handles a selection reaching into the container", () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "before", type: "paragraph", content: "Before" },
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "Title",
+        children: [
+          { id: "t-p-0", type: "paragraph", content: "First" },
+          { id: "t-p-1", type: "paragraph", content: "Second" },
+        ],
+      },
+    ]);
+    editor.setSelection("before", "t-p-0");
+
+    const result = editor.getSelectionCutBlocks();
+    // The container is partially covered, so its included children are
+    // spliced in rather than the container being returned whole.
+    expect(result.blocks.map((block) => block.id)).toEqual(["before", "t-p-0"]);
+  });
+
+  it("getSelectionCutBlocks handles a selection ending inside the title", () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "before", type: "paragraph", content: "Before" },
+      {
+        type: "toggle",
+        id: "t-0",
+        content: "Title",
+        children: [
+          { id: "t-p-0", type: "paragraph", content: "First" },
+          { id: "t-p-1", type: "paragraph", content: "Second" },
+        ],
+      },
+    ]);
+    editor.setSelection("before", "t-0");
+
+    // The selection ends inside the container's own title, before any of its
+    // children — so the generated `__children` node is absent from the slice.
+    // Converting the container must not throw; it comes back as a cut block
+    // (its title, no children) rather than recursing into its content node.
+    const result = editor.getSelectionCutBlocks();
+    expect(result.blocks.map((block) => block.id)).toEqual(["before", "t-0"]);
+    expect(result.blockCutAtEnd).toBe("t-0");
+    const toggle = result.blocks.find((block) => block.id === "t-0")!;
+    expect(toggle.children).toEqual([]);
+  });
+});
diff --git a/packages/core/src/api/blockManipulation/containers/fixContainer.ts b/packages/core/src/api/blockManipulation/containers/fixContainer.ts
new file mode 100644
index 0000000000..a756da8573
--- /dev/null
+++ b/packages/core/src/api/blockManipulation/containers/fixContainer.ts
@@ -0,0 +1,244 @@
+import { Fragment, Slice, type Node, type NodeType } from "prosemirror-model";
+import { type Transaction } from "prosemirror-state";
+import { ReplaceAroundStep } from "prosemirror-transform";
+import type { Schema } from "prosemirror-model";
+
+import {
+  blockTypeOfContainerChildrenNode,
+  getChildrenConfig,
+  isContentContainerNode,
+  resolveChildren,
+} from "../../../schema/blocks/children.js";
+import { getNodeById } from "../../nodeUtil.js";
+import { getBlockSchema, getPmSchema } from "../../pmUtil.js";
+
+export function isContainerNode(type: NodeType): boolean {
+  return type.isInGroup("childContainer") && type.name !== "blockGroup";
+}
+
+export function isEmptyContainerChild(node: Node): boolean {
+  if (node.type.name === "blockContainer") {
+    const blockContent = node.firstChild;
+    return (
+      node.childCount === 1 &&
+      !!blockContent &&
+      blockContent.type.name === "paragraph" &&
+      blockContent.childCount === 0
+    );
+  }
+  if (isContainerNode(node.type)) {
+    return node.childCount === 1 && isEmptyContainerChild(node.firstChild!);
+  }
+  return false;
+}
+
+export function removeEmptyChildren(tr: Transaction, containerPos: number) {
+  const container = tr.doc.resolve(containerPos).nodeAfter;
+  if (!container || !isContainerNode(container.type)) {
+    throw new Error(
+      "Invalid containerPos: does not point to a container node.",
+    );
+  }
+
+  for (
+    let childIndex = container.childCount - 1;
+    childIndex >= 0;
+    childIndex--
+  ) {
+    const childPos = tr.doc.resolve(containerPos + 1).posAtIndex(childIndex);
+    const child = tr.doc.resolve(childPos).nodeAfter;
+    if (!child) {
+      throw new Error("Invalid childPos: does not point to a child node.");
+    }
+
+    if (isEmptyContainerChild(child)) {
+      tr.delete(childPos, childPos + child.nodeSize);
+    }
+  }
+}
+
+function isInsertableChild(node: Node): boolean {
+  return (
+    node.type.name === "blockContainer" ||
+    node.type.isInGroup("blockGroupChild")
+  );
+}
+
+type ContainerRepairTarget = {
+  blockType: string;
+  blockPos: number;
+  blockNode: Node;
+  childrenPos: number;
+  contentNode: Node | undefined;
+};
+
+function getContainerRepairTarget(
+  doc: Node,
+  containerPos: number,
+): ContainerRepairTarget | undefined {
+  const node = doc.resolve(containerPos).nodeAfter;
+  if (!node) {
+    return undefined;
+  }
+
+  if (isContentContainerNode(node)) {
+    const contentNode = node.firstChild!;
+    return {
+      blockType: node.type.name,
+      blockPos: containerPos,
+      blockNode: node,
+      childrenPos: containerPos + 1 + contentNode.nodeSize,
+      contentNode,
+    };
+  }
+
+  if (!isContainerNode(node.type)) {
+    return undefined;
+  }
+
+  // A `__children` node: normalize to the block that owns it.
+  if (blockTypeOfContainerChildrenNode(node.type.name)) {
+    return getContainerRepairTarget(doc, doc.resolve(containerPos).before());
+  }
+
+  return {
+    blockType: node.type.name,
+    blockPos: containerPos,
+    blockNode: node,
+    childrenPos: containerPos,
+    contentNode: undefined,
+  };
+}
+
+export function fixContainer(tr: Transaction, containerPos: number) {
+  const target = getContainerRepairTarget(tr.doc, containerPos);
+  if (!target) {
+    throw new Error(
+      "Invalid containerPos: does not point to a container node.",
+    );
+  }
+
+  const blockConfig = getBlockSchema(getPmSchema(tr))[target.blockType];
+  const childrenConfig = blockConfig
+    ? getChildrenConfig(blockConfig)
+    : undefined;
+  const config = childrenConfig ? resolveChildren(childrenConfig) : undefined;
+
+  if (!config?.unwrapWhenEmptied) {
+    return;
+  }
+
+  // Don't silently destroy non-empty content.
+  if (target.contentNode && target.contentNode.content.size > 0) {
+    return;
+  }
+
+  removeEmptyChildren(tr, target.childrenPos);
+
+  const refreshedBlock = tr.doc.resolve(target.blockPos).nodeAfter;
+  if (!refreshedBlock || refreshedBlock.type !== target.blockNode.type) {
+    return;
+  }
+
+  // Where the (possibly shrunk) children now live, and where they start.
+  const refreshedChildren = target.contentNode
+    ? refreshedBlock.lastChild!
+    : refreshedBlock;
+  const childrenStart = target.contentNode
+    ? target.blockPos + 1 + refreshedBlock.firstChild!.nodeSize + 1
+    : target.blockPos + 1;
+
+  const min = config.minCount;
+
+  const nonEmptyChildren: { child: Node; offset: number }[] = [];
+  refreshedChildren.forEach((child, offset) => {
+    if (!isEmptyContainerChild(child)) {
+      nonEmptyChildren.push({ child, offset });
+    }
+  });
+
+  if (nonEmptyChildren.length >= min) {
+    return;
+  }
+
+  const blockEnd = target.blockPos + refreshedBlock.nodeSize;
+
+  if (nonEmptyChildren.length === 0) {
+    tr.delete(target.blockPos, blockEnd);
+    return;
+  }
+
+  // Unwrap: replace the container with its remaining non-empty children.
+  if (nonEmptyChildren.length === 1) {
+    const { child, offset } = nonEmptyChildren[0];
+    const childStart = childrenStart + offset;
+
+    const [gapFrom, gapTo] = isInsertableChild(child)
+      ? [childStart, childStart + child.nodeSize]
+      : [childStart + 1, childStart + child.nodeSize - 1];
+
+    tr.step(
+      new ReplaceAroundStep(
+        target.blockPos,
+        blockEnd,
+        gapFrom,
+        gapTo,
+        Slice.empty,
+        0,
+        false,
+      ),
+    );
+    return;
+  }
+
+  // Several survivors but still below `min`: rebuild replacement content.
+  const replacement: Node[] = [];
+  for (const { child } of nonEmptyChildren) {
+    if (isInsertableChild(child)) {
+      replacement.push(child);
+    } else {
+      child.forEach((grandChild) => replacement.push(grandChild));
+    }
+  }
+  tr.replaceWith(target.blockPos, blockEnd, Fragment.from(replacement));
+}
+
+export function fixContainersById(
+  tr: Transaction,
+  containers: { id: string; depth: number }[],
+) {
+  [...containers]
+    .sort((a, b) => b.depth - a.depth)
+    .forEach(({ id }) => {
+      const target = getNodeById(id, tr.doc);
+      if (!target) {
+        return;
+      }
+      fixContainer(tr, target.posBeforeNode);
+    });
+}
+
+export function flattenNonInsertableBlocks<
+  T extends { type?: string; content?: unknown; children?: T[] },
+>(blocks: T[], pmSchema: Schema): T[] {
+  return blocks.flatMap((block) => {
+    const nodeType = block.type ? pmSchema.nodes[block.type] : undefined;
+    if (
+      nodeType &&
+      nodeType.isInGroup("bnBlock") &&
+      !nodeType.isInGroup("blockGroupChild")
+    ) {
+      const children = flattenNonInsertableBlocks(
+        block.children ?? [],
+        pmSchema,
+      );
+      return Array.isArray(block.content) && block.content.length > 0
+        ? [
+            { type: "paragraph", content: block.content } as unknown as T,
+            ...children,
+          ]
+        : children;
+    }
+    return [block];
+  });
+}
diff --git a/packages/core/src/api/blockManipulation/selections/selection.ts b/packages/core/src/api/blockManipulation/selections/selection.ts
index d6229a3f0a..466845d94a 100644
--- a/packages/core/src/api/blockManipulation/selections/selection.ts
+++ b/packages/core/src/api/blockManipulation/selections/selection.ts
@@ -169,15 +169,12 @@ export function setSelection(
       headBlockInfo.blockNoteType as keyof typeof schema.blockSchema
     ];
 
-  if (
-    !anchorBlockInfo.isBlockContainer ||
-    anchorBlockConfig.content === "none"
-  ) {
+  if (!anchorBlockInfo.isWrappedBlock || anchorBlockConfig.content === "none") {
     throw new Error(
       `Attempting to set selection anchor in block without content (id ${startBlockId})`,
     );
   }
-  if (!headBlockInfo.isBlockContainer || headBlockConfig.content === "none") {
+  if (!headBlockInfo.isWrappedBlock || headBlockConfig.content === "none") {
     throw new Error(
       `Attempting to set selection anchor in block without content (id ${endBlockId})`,
     );
diff --git a/packages/core/src/api/blockManipulation/selections/textCursorPosition.ts b/packages/core/src/api/blockManipulation/selections/textCursorPosition.ts
index b0b2cc078d..38ad256457 100644
--- a/packages/core/src/api/blockManipulation/selections/textCursorPosition.ts
+++ b/packages/core/src/api/blockManipulation/selections/textCursorPosition.ts
@@ -74,7 +74,7 @@ export function setTextCursorPosition(
   const contentType: "none" | "inline" | "table" | "plain" =
     schema.blockSchema[info.blockNoteType]!.content;
 
-  if (info.isBlockContainer) {
+  if (info.isWrappedBlock) {
     const blockContent = info.blockContent;
     if (contentType === "none") {
       tr.setSelection(NodeSelection.create(tr.doc, blockContent.beforePos));
@@ -110,8 +110,15 @@ export function setTextCursorPosition(
   } else {
     const child =
       placement === "start"
-        ? info.childContainer.node.firstChild!
-        : info.childContainer.node.lastChild!;
+        ? info.childContainer.node.firstChild
+        : info.childContainer.node.lastChild;
+
+    if (!child) {
+      // A container allowed to hold no children has no text to put a cursor
+      // in, so the container itself is selected instead.
+      tr.setSelection(NodeSelection.create(tr.doc, info.bnBlock.beforePos));
+      return;
+    }
 
     setTextCursorPosition(tr, getNodeId(child, tr.doc), placement);
   }
diff --git a/packages/core/src/api/exporters/html/util/serializeBlocksExternalHTML.ts b/packages/core/src/api/exporters/html/util/serializeBlocksExternalHTML.ts
index e2274140f7..e1e72cf696 100644
--- a/packages/core/src/api/exporters/html/util/serializeBlocksExternalHTML.ts
+++ b/packages/core/src/api/exporters/html/util/serializeBlocksExternalHTML.ts
@@ -6,8 +6,10 @@ import {
   BlockImplementation,
   BlockSchema,
   InlineContentSchema,
+  isContainerType,
   StyleSchema,
 } from "../../../../schema/index.js";
+import { fillContainerAttributes } from "../../../../schema/blocks/containerAttributes.js";
 import { UnreachableCaseError } from "../../../../util/typescript.js";
 import {
   inlineContentToNodes,
@@ -270,6 +272,21 @@ function serializeBlock<
     }
     elementFragment.append(...Array.from(ret.dom.childNodes));
   } else {
+    // Asked of the block config rather than of its ProseMirror node — see the
+    // same check in `serializeBlocksInternalHTML`.
+    if (isContainerType(editor.schema.blockSchema[block.type as any])) {
+      // Container blocks own their outer DOM. Make sure the attributes
+      // needed to parse the HTML back (the type marker and non-default
+      // props, in the same `data-*` convention `propsToAttributes` reads)
+      // are present even when the block's render didn't add them.
+      // Author-set attributes win.
+      fillContainerAttributes(
+        ret.dom as HTMLElement,
+        block.type!,
+        props,
+        editor.schema.blockSchema[block.type as any].propSchema,
+      );
+    }
     elementFragment.append(ret.dom);
     if (nestingLevel > 0) {
       (ret.dom as HTMLElement).setAttribute(
@@ -297,15 +314,23 @@ function serializeBlock<
     // round trip, we fill their content with a placeholder character that the
     // parser strips out again (see `EMPTY_BLOCK_PLACEHOLDER`).
     //
-    // Only applies to blocks that hold inline content: containers (columns,
-    // tables) fill their `contentDOM` with child blocks later on, and code
-    // blocks would turn the placeholder into literal content.
+    // Only applies to blocks that hold inline content: pure containers
+    // (columns, tables) fill their `contentDOM` with child blocks later on,
+    // and code blocks would turn the placeholder into literal content.
+    //
+    // A container that has its *own* content needs the placeholder for a
+    // second reason, and its outer node isn't `inlineContent` so it needs its
+    // own check: that node's content is `<type>__content <type>__children`, so
+    // a parser reading a block element first has nothing to satisfy the
+    // content node with and cannot open the children node — every child then
+    // lands *after* the container instead of inside it. A leading text node is
+    // what opens the content node.
     const blockNodeType = editor.pmSchema.nodes[block.type as any];
-    if (
-      blockNodeType?.inlineContent &&
-      !blockNodeType.spec.code &&
-      ret.contentDOM.childNodes.length === 0
-    ) {
+    const blockConfig = editor.schema.blockSchema[block.type as any];
+    const needsPlaceholder = blockNodeType?.inlineContent
+      ? !blockNodeType.spec.code
+      : isContainerType(blockConfig) && blockConfig.content !== "none";
+    if (needsPlaceholder && ret.contentDOM.childNodes.length === 0) {
       ret.contentDOM.appendChild(doc.createTextNode(EMPTY_BLOCK_PLACEHOLDER));
     }
   }
diff --git a/packages/core/src/api/exporters/html/util/serializeBlocksInternalHTML.ts b/packages/core/src/api/exporters/html/util/serializeBlocksInternalHTML.ts
index 0f890b77ab..04113a013e 100644
--- a/packages/core/src/api/exporters/html/util/serializeBlocksInternalHTML.ts
+++ b/packages/core/src/api/exporters/html/util/serializeBlocksInternalHTML.ts
@@ -5,8 +5,10 @@ import type { BlockNoteEditor } from "../../../../editor/BlockNoteEditor.js";
 import {
   BlockSchema,
   InlineContentSchema,
+  isContainerType,
   StyleSchema,
 } from "../../../../schema/index.js";
+import { fillContainerAttributes } from "../../../../schema/blocks/containerAttributes.js";
 import { UnreachableCaseError } from "../../../../util/typescript.js";
 import {
   inlineContentToNodes,
@@ -126,6 +128,30 @@ export function serializeInlineContentInternalHTML<
   return fragment;
 }
 
+/**
+ * Appends the two region elements a content-bearing container's generated
+ * `__content` / `__children` nodes render, so that internal HTML matches what
+ * the editor puts in the DOM (and what the generated parse rules match).
+ */
+function createContainerRegions(
+  contentDOM: HTMLElement,
+  blockType: string,
+  options?: { document?: Document },
+): { content: HTMLElement; children: HTMLElement } {
+  const doc = options?.document ?? document;
+
+  const content = doc.createElement("div");
+  content.className = "bn-inline-content";
+  content.setAttribute("data-content-type", blockType);
+
+  const children = doc.createElement("div");
+  children.setAttribute("data-children-of", blockType);
+
+  contentDOM.append(content, children);
+
+  return { content, children };
+}
+
 function serializeBlock<
   BSchema extends BlockSchema,
   I extends InlineContentSchema,
@@ -159,7 +185,28 @@ function serializeBlock<
     editor as any,
   );
 
-  if (ret.contentDOM && block.content) {
+  // Asked of the block config rather than of its ProseMirror node: a container
+  // that has its own content compiles to an outer node holding a separate
+  // children node, so the outer node is not itself a `childContainer` — but
+  // the block is still a container and still owns its outer DOM.
+  const blockConfig = editor.schema.blockSchema[block.type as any];
+  const isContainer = isContainerType(blockConfig);
+
+  // A container with its own content holds two nodes — the generated
+  // `__content` and `__children` — and so renders two region elements inside
+  // its content host. They are not decoration: without them only the *first*
+  // child parses back inside the container. ProseMirror has to invent the
+  // `__children` wrapping while parsing, and `blockContainer`'s `blockOuter`
+  // skip rule re-syncs the parse context to the container afterwards, closing
+  // that invented wrapping again.
+  const regions =
+    isContainer && ret.contentDOM && blockConfig.content !== "none"
+      ? createContainerRegions(ret.contentDOM, block.type!, options)
+      : undefined;
+
+  const contentHost = regions?.content ?? ret.contentDOM;
+
+  if (contentHost && block.content) {
     const ic = serializeInlineContentInternalHTML(
       editor,
       block.content as any, // TODO
@@ -167,12 +214,25 @@ function serializeBlock<
       block.type,
       options,
     );
-    ret.contentDOM.appendChild(ic);
+    contentHost.appendChild(ic);
   }
 
-  const pmType = editor.pmSchema.nodes[block.type as any];
+  if (isContainer) {
+    // Container blocks own their outer DOM. Internal HTML must round-trip
+    // losslessly, so make sure the attributes the generated parse rules read
+    // (the type marker and non-default props as `data-*`) are present even
+    // when the block's render didn't add them. Author-set attributes win.
+    fillContainerAttributes(
+      ret.dom as HTMLElement,
+      block.type!,
+      props,
+      blockConfig.propSchema,
+    );
 
-  if (pmType.isInGroup("bnBlock")) {
+    // A pure container holds its children directly in its `contentDOM`; one
+    // with its own content puts them in the children region, after the content
+    // region — the reading order the document model itself imposes.
+    const childrenHost = regions?.children ?? ret.contentDOM;
     if (block.children && block.children.length > 0) {
       const fragment = serializeBlocks(
         editor,
@@ -181,7 +241,7 @@ function serializeBlock<
         options,
       );
 
-      ret.contentDOM?.append(fragment);
+      childrenHost?.append(fragment);
     }
     return ret.dom;
   }
diff --git a/packages/core/src/api/getBlockInfoFromPos.ts b/packages/core/src/api/getBlockInfoFromPos.ts
index 04ed789c98..667e32673d 100644
--- a/packages/core/src/api/getBlockInfoFromPos.ts
+++ b/packages/core/src/api/getBlockInfoFromPos.ts
@@ -1,6 +1,11 @@
 import { Node, ResolvedPos } from "prosemirror-model";
 import { EditorState, Transaction } from "prosemirror-state";
 
+import {
+  CHILD_CONTAINER_GROUP,
+  CONTAINER_CONTENT_GROUP,
+} from "../schema/blocks/children.js";
+
 type SingleBlockInfo = {
   node: Node;
   beforePos: number;
@@ -20,13 +25,16 @@ export type BlockInfo = {
   blockNoteType: string;
 } & (
   | {
-      // In case we're not dealing with a BlockContainer, we're dealing with a "wrapper node" (like a Column or ColumnList), so it will always have children
+      // A container block (Column, ColumnList, a custom container): its own node
+      // holds its children directly, and it has no `blockContent` of its own.
 
       /**
-       * The Prosemirror node that holds block.children. For non-blockContainer, this node will be the same as bnBlock.
+       * The Prosemirror node that holds block.children. For a container block,
+       * this node is the same as bnBlock.
        */
       childContainer: SingleBlockInfo;
-      isBlockContainer: false;
+      blockContent?: undefined;
+      isWrappedBlock: false;
     }
   | {
       /**
@@ -38,9 +46,16 @@ export type BlockInfo = {
        */
       blockContent: SingleBlockInfo;
       /**
-       * Whether bnBlock is a blockContainer node
+       * Whether `bnBlock` wraps the block's content in a node of its own —
+       * either a `blockContainer` (an ordinary block wrapped for nesting), or
+       * a container block that has its own content as well as children. Both
+       * have the same shape: a content node, then an optional child container.
+       *
+       * Note this is roughly the *opposite* of "is a container block": a
+       * column has `isWrappedBlock: false`. Sites that need "is this literally
+       * a `blockContainer`" should read `bnBlock.node.type.name`.
        */
-      isBlockContainer: true;
+      isWrappedBlock: true;
     }
 );
 
@@ -183,48 +198,49 @@ export function getBlockInfoWithManualOffset(
     afterPos: bnBlockAfterPos,
   };
 
-  if (bnBlockNode.type.name === "blockContainer") {
+  // A container block that has its own content is shaped like a
+  // `blockContainer`: a content node followed by a node holding its children.
+  // Discriminating on that shape rather than on the node's name is what lets
+  // every branch written against `blockContainer` cover it too.
+  const isContentContainer = !!bnBlockNode.firstChild?.type.isInGroup(
+    CONTAINER_CONTENT_GROUP,
+  );
+
+  if (bnBlockNode.type.name === "blockContainer" || isContentContainer) {
     let blockContent: SingleBlockInfo | undefined;
-    let blockGroup: SingleBlockInfo | undefined;
+    let childContainer: SingleBlockInfo | undefined;
 
     bnBlockNode.forEach((node, offset) => {
-      if (node.type.spec.group === "blockContent") {
-        // console.log(beforePos, offset);
-        const blockContentNode = node;
-        const blockContentBeforePos = bnBlockBeforePos + offset + 1;
-        const blockContentAfterPos = blockContentBeforePos + node.nodeSize;
-
-        blockContent = {
-          node: blockContentNode,
-          beforePos: blockContentBeforePos,
-          afterPos: blockContentAfterPos,
-        };
-      } else if (node.type.name === "blockGroup") {
-        const blockGroupNode = node;
-        const blockGroupBeforePos = bnBlockBeforePos + offset + 1;
-        const blockGroupAfterPos = blockGroupBeforePos + node.nodeSize;
+      const beforePos = bnBlockBeforePos + offset + 1;
+      const afterPos = beforePos + node.nodeSize;
 
-        blockGroup = {
-          node: blockGroupNode,
-          beforePos: blockGroupBeforePos,
-          afterPos: blockGroupAfterPos,
-        };
+      if (
+        node.type.spec.group === "blockContent" ||
+        node.type.isInGroup(CONTAINER_CONTENT_GROUP)
+      ) {
+        blockContent = { node, beforePos, afterPos };
+      } else if (node.type.isInGroup(CHILD_CONTAINER_GROUP)) {
+        childContainer = { node, beforePos, afterPos };
       }
     });
 
     if (!blockContent) {
       throw new Error(
         // eslint-disable-next-line @typescript-eslint/restrict-template-expressions
-        `blockContainer node does not contain a blockContent node in its children: ${bnBlockNode}`,
+        `${bnBlockNode.type.name} node does not contain a content node in its children: ${bnBlockNode}`,
       );
     }
 
     return {
-      isBlockContainer: true,
+      isWrappedBlock: true,
       bnBlock,
       blockContent,
-      childContainer: blockGroup,
-      blockNoteType: blockContent.node.type.name,
+      childContainer,
+      // A `blockContainer` is a generic wrapper, so its type comes from the
+      // content node inside it. A container block *is* its own type.
+      blockNoteType: isContentContainer
+        ? bnBlockNode.type.name
+        : blockContent.node.type.name,
     };
   } else {
     if (!bnBlock.node.type.isInGroup("childContainer")) {
@@ -235,7 +251,7 @@ export function getBlockInfoWithManualOffset(
     }
 
     return {
-      isBlockContainer: false,
+      isWrappedBlock: false,
       bnBlock: bnBlock,
       childContainer: bnBlock,
       blockNoteType: bnBlock.node.type.name,
diff --git a/packages/core/src/api/nodeConversions/blockToNode.ts b/packages/core/src/api/nodeConversions/blockToNode.ts
index af5c0ba1b7..d32b040e45 100644
--- a/packages/core/src/api/nodeConversions/blockToNode.ts
+++ b/packages/core/src/api/nodeConversions/blockToNode.ts
@@ -1,4 +1,11 @@
-import { Attrs, Fragment, Mark, Node, Schema } from "@tiptap/pm/model";
+import {
+  Attrs,
+  Fragment,
+  Mark,
+  Node,
+  NodeType,
+  Schema,
+} from "@tiptap/pm/model";
 
 import UniqueID from "../../extensions/tiptap-extensions/UniqueID/UniqueID.js";
 import type {
@@ -16,10 +23,20 @@ import {
   isPartialLinkInlineContent,
   isStyledTextInlineContent,
 } from "../../schema/inlineContent/types.js";
+import {
+  getChildrenConfig,
+  getContentContainerNodeTypes,
+  resolveChildren,
+} from "../../schema/blocks/children.js";
+import { isContainerNode } from "../blockManipulation/containers/fixContainer.js";
 import { getColspan, isPartialTableCell } from "../../util/table.js";
 import { UnreachableCaseError } from "../../util/typescript.js";
 import { getAbsoluteTableCells } from "../blockManipulation/tables/tables.js";
-import { getStyleSchema, isPlainContentNodeType } from "../pmUtil.js";
+import {
+  getBlockSchema,
+  getStyleSchema,
+  isPlainContentNodeType,
+} from "../pmUtil.js";
 
 /**
  * Convert a StyledText inline element to a
@@ -334,6 +351,147 @@ function blockOrInlineContentToContentNode(
   return contentNode;
 }
 
+const EMPTY_SEEDING: ReadonlySet<string> = new Set();
+
+function unwrapsWhenEmptied(blockType: string, schema: Schema): boolean {
+  const blockConfig = getBlockSchema(schema)[blockType];
+  const children = blockConfig ? getChildrenConfig(blockConfig) : undefined;
+  return !!children && resolveChildren(children).unwrapWhenEmptied;
+}
+
+// `createAndFill` produces nodes with `id: null`; patch them before use.
+function withGeneratedIds(node: Node): Node {
+  if (node.isText) {
+    return node;
+  }
+
+  const children: Node[] = [];
+  let childChanged = false;
+  node.forEach((child) => {
+    const next = withGeneratedIds(child);
+    childChanged ||= next !== child;
+    children.push(next);
+  });
+
+  const needsId = node.type.isInGroup("bnBlock") && node.attrs.id === null;
+  if (!needsId && !childChanged) {
+    return node;
+  }
+
+  return node.type.create(
+    needsId ? { ...node.attrs, id: UniqueID.options.generateID() } : node.attrs,
+    childChanged ? Fragment.from(children) : node.content,
+    node.marks,
+  );
+}
+
+function seedDefaultChildren(
+  blockType: string,
+  schema: Schema,
+  styleSchema: StyleSchema,
+  seedingTypes: ReadonlySet<string>,
+): Node[] | undefined {
+  const blockSchemaConfig = getBlockSchema(schema)[blockType];
+  const childrenConfig = blockSchemaConfig
+    ? getChildrenConfig(blockSchemaConfig)
+    : undefined;
+
+  if (!childrenConfig) {
+    return undefined;
+  }
+
+  const defaultChildren = resolveChildren(childrenConfig).default;
+  if (!defaultChildren || defaultChildren.length === 0) {
+    return undefined;
+  }
+
+  if (seedingTypes.has(blockType)) {
+    throw new Error(
+      `Seeding "${blockType}" ends up seeding it again (${[...seedingTypes, blockType].join(" -> ")}). ` +
+        "Give the cyclic default explicit children, or remove the self-reference.",
+    );
+  }
+
+  const nextSeeding = new Set(seedingTypes).add(blockType);
+  return defaultChildren.map((child) =>
+    blockToNode(
+      child as PartialBlock<any, any, any>,
+      schema,
+      styleSchema,
+      nextSeeding,
+    ),
+  );
+}
+
+function partialContentToInlineNodes(
+  block: PartialBlock<any, any, any>,
+  contentNodeName: string,
+  schema: Schema,
+  styleSchema: StyleSchema,
+): Node[] {
+  if (block.content === undefined) {
+    return [];
+  }
+  if (typeof block.content === "string" || Array.isArray(block.content)) {
+    return inlineContentToNodes(
+      typeof block.content === "string" ? [block.content] : block.content,
+      schema,
+      contentNodeName,
+      styleSchema,
+    );
+  }
+
+  throw new Error(
+    `Block "${block.type}" cannot have content of type "${block.content.type}".`,
+  );
+}
+
+function createContainerChildrenNode(
+  blockType: string,
+  type: NodeType,
+  schema: Schema,
+  styleSchema: StyleSchema,
+  seedingTypes: ReadonlySet<string>,
+  attrs: Attrs | null = null,
+): Node {
+  const seeded = seedDefaultChildren(
+    blockType,
+    schema,
+    styleSchema,
+    seedingTypes,
+  );
+
+  if (!seeded && unwrapsWhenEmptied(blockType, schema)) {
+    return type.create(attrs);
+  }
+
+  const node = type.createAndFill(attrs, seeded);
+  if (!node) {
+    throw new Error(
+      `Cannot create block "${blockType}": its \`default\` children don't fit its \`children\` config ` +
+        `(it accepts \`${type.spec.content}\`).`,
+    );
+  }
+
+  return node;
+}
+
+// Skips `createAndFill` for unwrap-on-empty containers (fill would be undone
+// by the next repair pass) and for unfittable content (let `node.check()` report it).
+function createExplicitChildrenNode(
+  blockType: string,
+  type: NodeType,
+  schema: Schema,
+  children: Node[],
+  attrs: Attrs | null = null,
+): Node {
+  if (unwrapsWhenEmptied(blockType, schema)) {
+    return type.create(attrs, children);
+  }
+
+  return type.createAndFill(attrs, children) ?? type.create(attrs, children);
+}
+
 /**
  * Converts a BlockNote block to a Prosemirror node.
  */
@@ -341,6 +499,7 @@ export function blockToNode(
   block: PartialBlock<any, any, any>,
   schema: Schema,
   styleSchema: StyleSchema = getStyleSchema(schema),
+  seedingTypes: ReadonlySet<string> = EMPTY_SEEDING,
 ) {
   let id = block.id;
 
@@ -352,7 +511,7 @@ export function blockToNode(
 
   if (block.children) {
     for (const child of block.children) {
-      children.push(blockToNode(child, schema, styleSchema));
+      children.push(blockToNode(child, schema, styleSchema, seedingTypes));
     }
   }
 
@@ -360,9 +519,11 @@ export function blockToNode(
     !block.type || // can happen if block.type is not defined (this should create the default node)
     schema.nodes[block.type].isInGroup("blockContent");
 
-  if (isBlockContent) {
-    // Blocks with a type that matches "blockContent" group always need to be wrapped in a blockContainer
+  const contentContainerTypes = block.type
+    ? getContentContainerNodeTypes(schema, block.type)
+    : undefined;
 
+  if (isBlockContent) {
     const contentNode = blockOrInlineContentToContentNode(
       block,
       schema,
@@ -381,15 +542,53 @@ export function blockToNode(
       },
       groupNode ? [contentNode, groupNode] : contentNode,
     );
-  } else if (schema.nodes[block.type].isInGroup("bnBlock")) {
-    // `create` (not `createChecked`) so partial container blocks pass through;
-    // callers that mutate the doc validate via `node.check()` before inserting.
-    return schema.nodes[block.type].create(
-      {
-        id: id,
-        ...block.props,
-      },
-      children,
+  } else if (contentContainerTypes) {
+    // A container with its own content: the content and the children each get
+    // a node of their own, since a ProseMirror node holds either inline
+    // content or block content but never both.
+    const { contentType, childrenType } = contentContainerTypes;
+
+    const contentNode = contentType.createChecked(
+      null,
+      partialContentToInlineNodes(block, contentType.name, schema, styleSchema),
+    );
+
+    const childrenNode =
+      block.children !== undefined
+        ? createExplicitChildrenNode(block.type, childrenType, schema, children)
+        : createContainerChildrenNode(
+            block.type,
+            childrenType,
+            schema,
+            styleSchema,
+            seedingTypes,
+          );
+
+    return withGeneratedIds(
+      schema.nodes[block.type].create({ id: id, ...block.props }, [
+        contentNode,
+        childrenNode,
+      ]),
+    );
+  } else if (isContainerNode(schema.nodes[block.type])) {
+    const type = schema.nodes[block.type];
+    const attrs = { id: id, ...block.props };
+
+    if (block.children !== undefined) {
+      return withGeneratedIds(
+        createExplicitChildrenNode(block.type, type, schema, children, attrs),
+      );
+    }
+
+    return withGeneratedIds(
+      createContainerChildrenNode(
+        block.type,
+        type,
+        schema,
+        styleSchema,
+        seedingTypes,
+        attrs,
+      ),
     );
   } else {
     throw new Error(
diff --git a/packages/core/src/api/nodeConversions/contentContainers.test.ts b/packages/core/src/api/nodeConversions/contentContainers.test.ts
new file mode 100644
index 0000000000..9bd12a90a5
--- /dev/null
+++ b/packages/core/src/api/nodeConversions/contentContainers.test.ts
@@ -0,0 +1,429 @@
+// @vitest-environment node
+import type { Node, Schema } from "@tiptap/pm/model";
+import { afterAll, beforeAll, describe, expect, it } from "vite-plus/test";
+
+import { BlockNoteSchema } from "../../blocks/BlockNoteSchema.js";
+import { defaultBlockSpecs } from "../../blocks/defaultBlocks.js";
+import { BlockNoteEditor } from "../../editor/BlockNoteEditor.js";
+import { createBlockSpec } from "../../schema/blocks/createSpec.js";
+import {
+  getBottomNestedBlockInfo,
+  getPrevBlockInfo,
+} from "../blockManipulation/commands/mergeBlocks/mergeBlocks.js";
+import { getBlockInfoWithManualOffset } from "../getBlockInfoFromPos.js";
+import { blockToNode } from "./blockToNode.js";
+import { nodeToBlock } from "./nodeToBlock.js";
+
+// A container block with its own inline content: the toggle shape. Its node
+// holds a generated content node and a generated children node, which is what
+// makes its `Block` JSON identical to a nested regular block's.
+// Nothing here is ever rendered — this suite works on nodes and a headless
+// editor's schema — so `render` only has to exist for the spec to be accepted.
+const notRendered = () => {
+  throw new Error("not rendered in this suite");
+};
+
+const Toggle = createBlockSpec(
+  {
+    type: "toggle" as const,
+    propSchema: { open: { default: true } },
+    content: "inline",
+    children: {},
+  },
+  { render: notRendered },
+)();
+
+// The same, but allowed to have no children at all.
+const OptionalToggle = createBlockSpec(
+  {
+    type: "optionalToggle" as const,
+    propSchema: {},
+    content: "inline",
+    children: { min: 0 },
+  },
+  { render: notRendered },
+)();
+
+// A pure container, to pair each content-bearing container against.
+const containerSpec = <TName extends string>(
+  type: TName,
+  config: { content: "none" | "inline"; children: any; placement?: any },
+) =>
+  createBlockSpec(
+    {
+      type,
+      propSchema: {},
+      ...config,
+    } as any,
+    { render: notRendered },
+  )();
+
+// Pairs of (pure container, content-bearing container) sharing one `children`
+// config. Their content expressions must match: the same generator runs for
+// both, so every `allow`/`min`/`max`/`sequence` option enforces identically.
+const CHILDREN_CONFIGS = {
+  Default: {},
+  Bounded: { min: 0, max: 3 },
+  Restricted: { allow: { blocks: false, containers: ["cell"] }, min: 2 },
+  Sequenced: {
+    sequence: [
+      { allow: { blocks: false, containers: ["cell"] } },
+      { count: { min: 1 } },
+    ],
+  },
+} as const;
+
+const schema = BlockNoteSchema.create().extend({
+  blockSpecs: {
+    ...defaultBlockSpecs,
+    toggle: Toggle,
+    optionalToggle: OptionalToggle,
+    cell: containerSpec("cell", { content: "none", children: {} }),
+    pureDefault: containerSpec("pureDefault", {
+      content: "none",
+      children: CHILDREN_CONFIGS.Default,
+    }),
+    contentDefault: containerSpec("contentDefault", {
+      content: "inline",
+      children: CHILDREN_CONFIGS.Default,
+    }),
+    pureBounded: containerSpec("pureBounded", {
+      content: "none",
+      children: CHILDREN_CONFIGS.Bounded,
+    }),
+    contentBounded: containerSpec("contentBounded", {
+      content: "inline",
+      children: CHILDREN_CONFIGS.Bounded,
+    }),
+    pureRestricted: containerSpec("pureRestricted", {
+      content: "none",
+      children: CHILDREN_CONFIGS.Restricted,
+    }),
+    contentRestricted: containerSpec("contentRestricted", {
+      content: "inline",
+      children: CHILDREN_CONFIGS.Restricted,
+    }),
+    pureSequenced: containerSpec("pureSequenced", {
+      content: "none",
+      children: CHILDREN_CONFIGS.Sequenced,
+    }),
+    contentSequenced: containerSpec("contentSequenced", {
+      content: "inline",
+      children: CHILDREN_CONFIGS.Sequenced,
+    }),
+  } as const,
+});
+
+let editor: BlockNoteEditor<any, any, any>;
+let pmSchema: Schema;
+
+beforeAll(() => {
+  editor = BlockNoteEditor.create({ schema }) as any;
+  pmSchema = editor.pmSchema;
+});
+
+afterAll(() => {
+  editor._tiptapEditor.destroy();
+  editor = undefined as any;
+});
+
+// `nodeToBlock(node, doc)` takes the containing document as its second
+// argument, so blocks built in isolation need a minimal valid doc around them.
+const wrapInDoc = (...blocks: Node[]): Node =>
+  pmSchema.nodes["doc"].createChecked(
+    null,
+    pmSchema.nodes["blockGroup"].createChecked(null, blocks),
+  );
+
+describe("content-bearing container: node shape", () => {
+  it("builds a content node and a children node inside the block's node", () => {
+    const node = blockToNode(
+      {
+        id: "t-0",
+        type: "toggle",
+        props: { open: false },
+        content: "Title",
+        children: [{ id: "c-0", type: "paragraph", content: "Child" }],
+      } as any,
+      pmSchema,
+    );
+
+    expect(node.type.name).toBe("toggle");
+    expect(node.type.isInGroup("bnBlock")).toBe(true);
+    expect(node.type.isInGroup("blockGroupChild")).toBe(true);
+    // The block's node is not itself a child container — the generated
+    // children node is.
+    expect(node.type.isInGroup("childContainer")).toBe(false);
+
+    expect(node.childCount).toBe(2);
+
+    const contentNode = node.child(0);
+    expect(contentNode.type.name).toBe("toggle__content");
+    expect(contentNode.type.isInGroup("containerContent")).toBe(true);
+    // Deliberately not `blockContent`: that group is what `blockContainer`
+    // accepts, so a paste could otherwise produce
+    // `blockContainer > toggle__content`.
+    expect(contentNode.type.isInGroup("blockContent")).toBe(false);
+    expect(contentNode.textContent).toBe("Title");
+
+    const childrenNode = node.child(1);
+    expect(childrenNode.type.name).toBe("toggle__children");
+    expect(childrenNode.type.isInGroup("childContainer")).toBe(true);
+    expect(childrenNode.childCount).toBe(1);
+    expect(childrenNode.child(0).type.name).toBe("blockContainer");
+
+    // The node is valid against the schema.
+    expect(() => node.check()).not.toThrow();
+  });
+
+  it("keeps all props (and the id) on the outer node", () => {
+    const node = blockToNode(
+      {
+        id: "t-0",
+        type: "toggle",
+        props: { open: false },
+        content: "Title",
+      } as any,
+      pmSchema,
+    );
+
+    expect(node.attrs.id).toBe("t-0");
+    expect(node.attrs.open).toBe(false);
+    expect("open" in node.child(0).attrs).toBe(false);
+    expect("id" in node.child(0).attrs).toBe(false);
+  });
+
+  it("auto-fills children when none are given", () => {
+    const node = blockToNode(
+      { id: "t-0", type: "toggle", content: "Title" } as any,
+      pmSchema,
+    );
+
+    const childrenNode = node.child(1);
+    expect(childrenNode.childCount).toBe(1);
+    // Auto-filled nodes come from the schema with `id: null`; they must be
+    // given real ids before they're converted back to blocks.
+    expect(childrenNode.child(0).attrs.id).toBeTruthy();
+  });
+});
+
+describe("content-bearing container: Block JSON", () => {
+  it("round-trips identically to a nested regular block", () => {
+    const toggleNode = blockToNode(
+      {
+        id: "b-0",
+        type: "toggle",
+        content: "Title",
+        children: [{ id: "c-0", type: "paragraph", content: "Child" }],
+      } as any,
+      pmSchema,
+    );
+    const paragraphNode = blockToNode(
+      {
+        id: "b-0",
+        type: "paragraph",
+        content: "Title",
+        children: [{ id: "c-0", type: "paragraph", content: "Child" }],
+      } as any,
+      pmSchema,
+    );
+
+    const toggleBlock = nodeToBlock(toggleNode, wrapInDoc(toggleNode));
+    const paragraphBlock = nodeToBlock(paragraphNode, wrapInDoc(paragraphNode));
+
+    expect(Object.keys(toggleBlock)).toEqual([
+      "id",
+      "type",
+      "props",
+      "content",
+      "children",
+    ]);
+    expect(Object.keys(toggleBlock)).toEqual(Object.keys(paragraphBlock));
+
+    // Everything but the block's own type and props is structurally identical
+    // to the nested paragraph's.
+    const { type: _toggleType, props: _toggleProps, ...toggle } = toggleBlock;
+    const {
+      type: _paragraphType,
+      props: _paragraphProps,
+      ...paragraph
+    } = paragraphBlock;
+    expect(toggle).toEqual(paragraph);
+
+    expect(toggleBlock).toEqual({
+      id: "b-0",
+      type: "toggle",
+      props: { open: true },
+      content: [{ type: "text", text: "Title", styles: {} }],
+      children: [
+        {
+          id: "c-0",
+          type: "paragraph",
+          props: (paragraphBlock.children as any[])[0].props,
+          content: [{ type: "text", text: "Child", styles: {} }],
+          children: [],
+        },
+      ],
+    });
+  });
+
+  it("round-trips an empty container with no content", () => {
+    const node = blockToNode(
+      { id: "t-0", type: "optionalToggle", children: [] } as any,
+      pmSchema,
+    );
+    const block = nodeToBlock(node, wrapInDoc(node));
+
+    expect(block.content).toEqual([]);
+    expect(block.children).toEqual([]);
+  });
+});
+
+describe("content-bearing container: BlockInfo", () => {
+  it("is a wrapped block, with the content and children nodes resolved", () => {
+    const node = blockToNode(
+      {
+        id: "t-0",
+        type: "toggle",
+        content: "Title",
+        children: [{ id: "c-0", type: "paragraph", content: "Child" }],
+      } as any,
+      pmSchema,
+    );
+
+    const info = getBlockInfoWithManualOffset(node, 0);
+
+    // Structurally identical to a `blockContainer`, so every keyboard branch
+    // written against one covers this too.
+    expect(info.isWrappedBlock).toBe(true);
+    expect(info.blockContent!.node.type.name).toBe("toggle__content");
+    expect(info.childContainer!.node.type.name).toBe("toggle__children");
+    // The type comes from the outer node — a `blockContainer` is a generic
+    // wrapper, but a container block *is* its own type.
+    expect(info.blockNoteType).toBe("toggle");
+
+    // Positions are those of the nodes themselves.
+    expect(info.bnBlock.beforePos).toBe(0);
+    expect(info.blockContent!.beforePos).toBe(1);
+    expect(info.blockContent!.afterPos).toBe(1 + node.child(0).nodeSize);
+    expect(info.childContainer!.beforePos).toBe(1 + node.child(0).nodeSize);
+  });
+
+  it("still reads a blockContainer's type from its content node", () => {
+    const node = blockToNode(
+      { id: "p-0", type: "paragraph", content: "Hello" } as any,
+      pmSchema,
+    );
+
+    const info = getBlockInfoWithManualOffset(node, 0);
+    expect(info.isWrappedBlock).toBe(true);
+    expect(info.bnBlock.node.type.name).toBe("blockContainer");
+    expect(info.blockNoteType).toBe("paragraph");
+  });
+
+  it("handles a container with zero children", () => {
+    const paragraphNode = blockToNode(
+      { id: "p-0", type: "paragraph", content: "Before" } as any,
+      pmSchema,
+    );
+    const toggleNode = blockToNode(
+      {
+        id: "t-0",
+        type: "optionalToggle",
+        content: "Title",
+        children: [],
+      } as any,
+      pmSchema,
+    );
+    const doc = wrapInDoc(paragraphNode, toggleNode);
+
+    const togglePos = 1 + paragraphNode.nodeSize;
+    const info = getBlockInfoWithManualOffset(toggleNode, togglePos);
+    expect(info.childContainer!.node.childCount).toBe(0);
+
+    // An empty child container has no last child to descend into, so the
+    // block itself is the bottom one.
+    expect(() => getBottomNestedBlockInfo(doc, info)).not.toThrow();
+    expect(getBottomNestedBlockInfo(doc, info).bnBlock.node).toBe(toggleNode);
+
+    expect(() => getPrevBlockInfo(doc, togglePos)).not.toThrow();
+    expect(getPrevBlockInfo(doc, togglePos)!.blockNoteType).toBe("paragraph");
+  });
+});
+
+describe("content-bearing container: in a headless editor", () => {
+  it("inserts and reads back", () => {
+    const headless = BlockNoteEditor.create({ schema }) as any;
+
+    try {
+      headless.replaceBlocks(headless.document, [
+        { id: "p-0", type: "paragraph", content: "Paragraph 0" },
+      ]);
+      headless.insertBlocks(
+        [
+          {
+            id: "t-0",
+            type: "toggle",
+            content: "Title",
+            children: [{ id: "c-0", type: "paragraph", content: "Child" }],
+          },
+        ],
+        "p-0",
+        "after",
+      );
+
+      const block = headless.getBlock("t-0")!;
+      expect(block.type).toBe("toggle");
+      expect(block.content).toEqual([
+        { type: "text", text: "Title", styles: {} },
+      ]);
+      expect(block.children.map((child: any) => child.id)).toEqual(["c-0"]);
+      // The child is an ordinary block of the document, reachable by id.
+      expect(headless.getBlock("c-0")).toBeDefined();
+      // The rendering half of this — that a container's attributes land on the
+      // author's own root element — is asserted against a real cascade in
+      // `tests/src/end-to-end/containerblocks/containerblocks.test.tsx`
+      // ("Stamps node type and id onto the author's own root element").
+    } finally {
+      headless._tiptapEditor.destroy();
+    }
+  });
+});
+
+describe("content-bearing container: children content expression", () => {
+  it.each(Object.keys(CHILDREN_CONFIGS))(
+    "%s compiles the same as it does for a pure container",
+    (name) => {
+      const pure = pmSchema.nodes[`pure${name}`];
+      const contentBearing = pmSchema.nodes[`content${name}__children`];
+
+      expect(contentBearing).toBeDefined();
+      expect(contentBearing.spec.content).toBe(pure.spec.content);
+    },
+  );
+
+  it("enforces the expression on the children node", () => {
+    // `Restricted` allows only `cell` children, and at least two of them.
+    expect(() =>
+      blockToNode(
+        {
+          type: "contentRestricted",
+          content: "Title",
+          children: [{ type: "paragraph" }],
+        } as any,
+        pmSchema,
+      ).check(),
+    ).toThrow();
+
+    expect(() =>
+      blockToNode(
+        {
+          type: "contentRestricted",
+          content: "Title",
+          children: [{ type: "cell" }, { type: "cell" }],
+        } as any,
+        pmSchema,
+      ).check(),
+    ).not.toThrow();
+  });
+});
diff --git a/packages/core/src/api/nodeConversions/fragmentToBlocks.ts b/packages/core/src/api/nodeConversions/fragmentToBlocks.ts
index 19f063d8bb..84c168e979 100644
--- a/packages/core/src/api/nodeConversions/fragmentToBlocks.ts
+++ b/packages/core/src/api/nodeConversions/fragmentToBlocks.ts
@@ -1,60 +1,98 @@
-import { Fragment } from "@tiptap/pm/model";
+import { Fragment, Node } from "@tiptap/pm/model";
 import {
   BlockNoDefaults,
   BlockSchema,
   InlineContentSchema,
   StyleSchema,
 } from "../../schema/index.js";
+import {
+  getChildrenConfig,
+  getMinChildCount,
+  isContentContainerNode,
+  isPlaceableAnywhere,
+} from "../../schema/blocks/children.js";
+import { isContainerNode } from "../blockManipulation/containers/fixContainer.js";
+import { getBlockSchema } from "../pmUtil.js";
 import { nodeToBlock } from "./nodeToBlock.js";
 
-/**
- * Converts all Blocks within a fragment to BlockNote blocks.
- */
+function getContainerChildren(
+  node: Node,
+): { blockType: string; children: Node } | undefined {
+  if (isContentContainerNode(node)) {
+    return { blockType: node.type.name, children: node.lastChild! };
+  }
+  if (isContainerNode(node.type)) {
+    return { blockType: node.type.name, children: node };
+  }
+  return undefined;
+}
+
+function isSelfContainedContainer(node: Node): boolean {
+  const container = getContainerChildren(node);
+  if (!container) {
+    return false;
+  }
+  const blockConfig =
+    getBlockSchema(node.type.schema)[container.blockType] ?? {};
+  const children = getChildrenConfig(blockConfig);
+  if (!children) {
+    return false;
+  }
+  return (
+    isPlaceableAnywhere(blockConfig) &&
+    container.children.childCount >= getMinChildCount(children)
+  );
+}
+
+function containerContentAsBlock<
+  B extends BlockSchema,
+  I extends InlineContentSchema,
+  S extends StyleSchema,
+>(node: Node, root: Node): BlockNoDefaults<B, I, S> | undefined {
+  if (!isContentContainerNode(node) || node.firstChild!.content.size === 0) {
+    return undefined;
+  }
+  const schema = node.type.schema;
+  const paragraph = schema.nodes["paragraph"].create(
+    null,
+    node.firstChild!.content,
+  );
+
+  return nodeToBlock(
+    schema.nodes["blockContainer"].createAndFill(null, paragraph)!,
+    root,
+  );
+}
+
 export function fragmentToBlocks<
   B extends BlockSchema,
   I extends InlineContentSchema,
   S extends StyleSchema,
 >(fragment: Fragment) {
-  // first convert selection to blocknote-style blocks, and then
-  // pass these to the exporter
   const blocks: BlockNoDefaults<B, I, S>[] = [];
+
+  const pushFlattened = (node: Node, root: Node) => {
+    const container = getContainerChildren(node);
+    if (container && !isSelfContainedContainer(node)) {
+      const content = containerContentAsBlock<B, I, S>(node, root);
+      if (content) {
+        blocks.push(content);
+      }
+      container.children.forEach((child) => pushFlattened(child, root));
+      return;
+    }
+    blocks.push(nodeToBlock(node, root));
+  };
+
   fragment.descendants((node) => {
     if (node.type.name === "blockContainer") {
       if (node.firstChild?.type.name === "blockGroup") {
-        // selection started within a block group
-        // in this case the fragment starts with:
-        // <blockContainer>
-        //   <blockGroup>
-        //     <blockContainer ... />
-        //     <blockContainer ... />
-        //   </blockGroup>
-        // </blockContainer>
-        //
-        // instead of:
-        // <blockContainer>
-        //   <blockContent ... />
-        //   <blockGroup>
-        //     <blockContainer ... />
-        //     <blockContainer ... />
-        //   </blockGroup>
-        // </blockContainer>
-        //
-        // so we don't need to serialize this block, just descend into the children of the blockGroup
         return true;
       }
     }
 
-    if (node.type.name === "columnList" && node.childCount === 1) {
-      // column lists with a single column should be flattened (not the entire column list has been selected)
-      node.firstChild?.forEach((child) => {
-        blocks.push(nodeToBlock(child, node));
-      });
-      return false;
-    }
-
     if (node.type.isInGroup("bnBlock")) {
-      blocks.push(nodeToBlock(node, node));
-      // don't descend into children, as they're already included in the block returned by nodeToBlock
+      pushFlattened(node, node);
       return false;
     }
     return true;
diff --git a/packages/core/src/api/nodeConversions/nodeToBlock.ts b/packages/core/src/api/nodeConversions/nodeToBlock.ts
index fead006657..e445c4e9e5 100644
--- a/packages/core/src/api/nodeConversions/nodeToBlock.ts
+++ b/packages/core/src/api/nodeConversions/nodeToBlock.ts
@@ -1,5 +1,7 @@
 import { Mark, Node, Slice } from "@tiptap/pm/model";
 import type { Block } from "../../blocks/defaultBlocks.js";
+import { isContainerNode } from "../blockManipulation/containers/fixContainer.js";
+import { isContentContainerNode } from "../../schema/blocks/children.js";
 import UniqueID from "../../extensions/tiptap-extensions/UniqueID/UniqueID.js";
 import type {
   BlockSchema,
@@ -430,7 +432,7 @@ export function nodeToBlock<
   const props: any = {};
   for (const [attr, value] of Object.entries({
     ...node.attrs,
-    ...(blockInfo.isBlockContainer ? blockInfo.blockContent.node.attrs : {}),
+    ...(blockInfo.isWrappedBlock ? blockInfo.blockContent.node.attrs : {}),
   })) {
     const propSchema = blockSpec.propSchema;
 
@@ -452,7 +454,7 @@ export function nodeToBlock<
   let content: Block<any, any, any>["content"];
 
   if (blockConfig.content === "inline") {
-    if (!blockInfo.isBlockContainer) {
+    if (!blockInfo.isWrappedBlock) {
       throw new Error("impossible");
     }
     content = contentNodeToInlineContent(
@@ -461,7 +463,7 @@ export function nodeToBlock<
       styleSchema,
     );
   } else if (blockConfig.content === "table") {
-    if (!blockInfo.isBlockContainer) {
+    if (!blockInfo.isWrappedBlock) {
       throw new Error("impossible");
     }
     content = contentNodeToTableContent(
@@ -470,7 +472,7 @@ export function nodeToBlock<
       styleSchema,
     );
   } else if (blockConfig.content === "plain") {
-    if (!blockInfo.isBlockContainer) {
+    if (!blockInfo.isWrappedBlock) {
       throw new Error("impossible");
     }
     // Plain content is a single unstyled text item; an empty block is an
@@ -533,6 +535,24 @@ export function docToBlocks<
  * </blockGroup>
  *
  */
+/**
+ * The node holding a bnBlock's children when that node holds them directly:
+ * the container itself for a pure container, its generated `__children` node
+ * for a container that also has its own content. `undefined` for a
+ * `blockContainer`, whose children live in an optional `blockGroup`.
+ */
+function getChildrenHolder(node: Node): Node | undefined {
+  if (isContentContainerNode(node)) {
+    // The children live in the generated `__children` node, which is the last
+    // child. When a slice boundary cuts through the container's own `__content`,
+    // the `__children` node is absent from the slice — its last (and only)
+    // child is then the `__content` node, which holds no children of its own.
+    const lastChild = node.lastChild;
+    return lastChild && isContainerNode(lastChild.type) ? lastChild : undefined;
+  }
+  return isContainerNode(node.type) ? node : undefined;
+}
+
 export function prosemirrorSliceToSlicedBlocks<
   BSchema extends BlockSchema,
   I extends InlineContentSchema,
@@ -563,7 +583,9 @@ export function prosemirrorSliceToSlicedBlocks<
     blockCutAtStart: string | undefined;
     blockCutAtEnd: string | undefined;
   } {
-    if (node.type.name !== "blockGroup") {
+    // Both `blockGroup` and container nodes (columnList, column, callout,
+    // ...) hold bnBlock children directly, so both can be processed here.
+    if (node.type.name !== "blockGroup" && !isContainerNode(node.type)) {
       throw new Error("unexpected");
     }
     const blocks: Block<BSchema, I, S>[] = [];
@@ -571,6 +593,68 @@ export function prosemirrorSliceToSlicedBlocks<
     let blockCutAtEnd: string | undefined;
 
     node.forEach((blockContainer, _offset, index) => {
+      const isFirstBlock = index === 0;
+      const isLastBlock = index === node.childCount - 1;
+
+      const childrenHolder = getChildrenHolder(blockContainer);
+      if (childrenHolder) {
+        // A container child. When the slice boundary is open inside it, the
+        // selection covers part of its children — skip the container wrapper
+        // and splice in the included children (mirroring the
+        // nested-blockGroup descent below). When fully enclosed, convert it
+        // wholesale.
+        const openAtStart = isFirstBlock && openStart > 0;
+        const openAtEnd = isLastBlock && openEnd > 0;
+
+        // A container that also has its own content keeps its children one
+        // node deeper, in its generated `__children` node.
+        const depthToChildren = childrenHolder === blockContainer ? 1 : 2;
+
+        if (openAtStart || openAtEnd) {
+          const ret = processNode(
+            childrenHolder,
+            openAtStart ? Math.max(0, openStart - depthToChildren) : 0,
+            openAtEnd ? Math.max(0, openEnd - depthToChildren) : 0,
+          );
+          if (openAtStart) {
+            blockCutAtStart = ret.blockCutAtStart;
+          }
+          if (openAtEnd) {
+            blockCutAtEnd = ret.blockCutAtEnd;
+          }
+          blocks.push(...ret.blocks);
+          return;
+        }
+
+        blocks.push(
+          nodeToBlock(blockContainer, slice.content.firstChild!) as Block<
+            BSchema,
+            I,
+            S
+          >,
+        );
+        return;
+      }
+
+      if (isContentContainerNode(blockContainer)) {
+        // A content-bearing container whose `__children` node is absent from
+        // the slice: the boundary cut through its own `__content`, so it has no
+        // children to splice in. Convert it wholesale (with its cut content),
+        // recording the cut boundary so callers know the block was sliced.
+        const block = nodeToBlock(
+          blockContainer,
+          slice.content.firstChild!,
+        ) as Block<BSchema, I, S>;
+        if (isFirstBlock && openStart > 0) {
+          blockCutAtStart = block.id;
+        }
+        if (isLastBlock && openEnd > 0) {
+          blockCutAtEnd = block.id;
+        }
+        blocks.push(block);
+        return;
+      }
+
       if (blockContainer.type.name !== "blockContainer") {
         throw new Error("unexpected");
       }
@@ -583,9 +667,6 @@ export function prosemirrorSliceToSlicedBlocks<
         );
       }
 
-      const isFirstBlock = index === 0;
-      const isLastBlock = index === node.childCount - 1;
-
       if (blockContainer.firstChild!.type.name === "blockGroup") {
         // this is the parent where a selection starts within one of its children,
         // e.g.:
diff --git a/packages/core/src/api/pmUtil.ts b/packages/core/src/api/pmUtil.ts
index 17ed2aa943..79461b75d1 100644
--- a/packages/core/src/api/pmUtil.ts
+++ b/packages/core/src/api/pmUtil.ts
@@ -2,6 +2,7 @@ import type { Node, NodeType, Schema } from "prosemirror-model";
 import { Transform } from "prosemirror-transform";
 import type { BlockNoteEditor } from "../editor/BlockNoteEditor.js";
 import { BlockNoteSchema } from "../blocks/BlockNoteSchema.js";
+import { blockTypeOfContainerContentNode } from "../schema/blocks/children.js";
 import type { BlockSchema } from "../schema/blocks/types.js";
 import type { InlineContentSchema } from "../schema/inlineContent/types.js";
 import type { StyleSchema } from "../schema/styles/types.js";
@@ -67,7 +68,16 @@ export function isPlainContentNodeType(
   schema: Schema,
   nodeType: NodeType,
 ): boolean {
-  if (getBlockSchema(schema)[nodeType.name]?.content === "plain") {
+  const blockSchema = getBlockSchema(schema);
+  // A content-bearing container's content lives in a generated node, so it
+  // isn't a key in the block schema — resolve it back to the block it belongs
+  // to.
+  const blockType =
+    blockTypeOfContainerContentNode(nodeType.name) ?? nodeType.name;
+
+  if (
+    (blockSchema[nodeType.name] ?? blockSchema[blockType])?.content === "plain"
+  ) {
     return true;
   }
 
diff --git a/packages/core/src/blocks/ListItem/ListItemKeyboardShortcuts.ts b/packages/core/src/blocks/ListItem/ListItemKeyboardShortcuts.ts
index 0b33335788..71f3ecaf35 100644
--- a/packages/core/src/blocks/ListItem/ListItemKeyboardShortcuts.ts
+++ b/packages/core/src/blocks/ListItem/ListItemKeyboardShortcuts.ts
@@ -11,7 +11,7 @@ export const handleEnter = (editor: BlockNoteEditor<any, any, any>) => {
     };
   });
 
-  if (!blockInfo.isBlockContainer) {
+  if (!blockInfo.isWrappedBlock) {
     return false;
   }
   const { bnBlock: blockContainer, blockContent } = blockInfo;
diff --git a/packages/core/src/blocks/ListItem/NumberedListItem/IndexingPlugin.ts b/packages/core/src/blocks/ListItem/NumberedListItem/IndexingPlugin.ts
index b268598218..5e52c8c76f 100644
--- a/packages/core/src/blocks/ListItem/NumberedListItem/IndexingPlugin.ts
+++ b/packages/core/src/blocks/ListItem/NumberedListItem/IndexingPlugin.ts
@@ -32,7 +32,7 @@ function calculateListItemIndex(
 
   // Fast path: previous sibling already in cache
   const blockInfo = getBlockInfo({ posBeforeNode: pos, node });
-  if (!blockInfo.isBlockContainer) {
+  if (!blockInfo.isWrappedBlock) {
     throw new Error("impossible");
   }
   const prevBlock = tr.doc.resolve(blockInfo.bnBlock.beforePos).nodeBefore;
@@ -80,7 +80,7 @@ function calculateListItemIndex(
     posBeforeNode: lastInChain.pos,
     node: lastInChain.node,
   });
-  if (!lastInfo.isBlockContainer) {
+  if (!lastInfo.isWrappedBlock) {
     throw new Error("impossible");
   }
   const predecessorNode = tr.doc.resolve(lastInfo.bnBlock.beforePos).nodeBefore;
diff --git a/packages/core/src/blocks/utils/listItemEnterHandler.ts b/packages/core/src/blocks/utils/listItemEnterHandler.ts
index 12e558a453..578d3aae8b 100644
--- a/packages/core/src/blocks/utils/listItemEnterHandler.ts
+++ b/packages/core/src/blocks/utils/listItemEnterHandler.ts
@@ -14,7 +14,7 @@ export const handleEnter = (
     };
   });
 
-  if (!blockInfo.isBlockContainer) {
+  if (!blockInfo.isWrappedBlock) {
     return false;
   }
   const { bnBlock: blockContainer, blockContent } = blockInfo;
diff --git a/packages/core/src/editor/BlockNoteEditor.ts b/packages/core/src/editor/BlockNoteEditor.ts
index 25b93d03f4..e631edb881 100644
--- a/packages/core/src/editor/BlockNoteEditor.ts
+++ b/packages/core/src/editor/BlockNoteEditor.ts
@@ -7,6 +7,7 @@ import {
 } from "@tiptap/core";
 import { type Command, type Transaction } from "@tiptap/pm/state";
 import { Node, Schema } from "prosemirror-model";
+import type { BlockPlacement } from "../api/blockManipulation/commands/insertBlocks/insertBlocks.js";
 import type { BlocksChanged } from "../api/getBlocksChangedByTransaction.js";
 import { blockToNode } from "../api/nodeConversions/blockToNode.js";
 import {
@@ -37,6 +38,7 @@ import type {
   StyleSchema,
   StyleSpecs,
 } from "../schema/index.js";
+import { assertContainerSchemaInvariants } from "../schema/blocks/assertSchemaInvariants.js";
 import "../style.css";
 import { mergeCSSClasses } from "../util/browser.js";
 import { EventEmitter } from "../util/EventEmitter.js";
@@ -558,6 +560,13 @@ export class BlockNoteEditor<
         tiptapOptions.parseOptions,
       );
 
+      // `blockToNode` is lenient, and `createDocument` builds from JSON without
+      // validating — so without this the one path that never checks its result
+      // is the one that seeds the whole document. A container below its
+      // `children.min` would reach the editor and stay there, where the same
+      // blocks passed to `insertBlocks` would have been rejected.
+      doc.check();
+
       this._tiptapEditor = new TiptapEditor({
         ...tiptapOptions,
         content: doc.toJSON(),
@@ -572,6 +581,8 @@ export class BlockNoteEditor<
 
     this.pmSchema.cached.blockNoteEditor = this;
 
+    assertContainerSchemaInvariants(this.pmSchema);
+
     this._tiptapEditor.on("mount", () => {
       this.headless = false;
     });
@@ -1051,13 +1062,14 @@ export class BlockNoteEditor<
    * error if the reference block could not be found.
    * @param blocksToInsert An array of partial blocks that should be inserted.
    * @param referenceBlock An identifier for an existing block, at which the new blocks should be inserted.
-   * @param placement Whether the blocks should be inserted just before, just after, or nested inside the
-   * `referenceBlock`.
+   * @param placement Where the blocks go relative to the `referenceBlock`: as its previous (`"before"`) or next
+   * (`"after"`) sibling, or nested inside it as its first (`"start"`) or last (`"end"`) children. Throws an error if
+   * the `referenceBlock` (or its parent, for `"before"`/`"after"`) doesn't accept the blocks there.
    */
   public insertBlocks(
     blocksToInsert: PartialBlock<BSchema, ISchema, SSchema>[],
     referenceBlock: BlockIdentifier,
-    placement: "before" | "after" = "before",
+    placement: BlockPlacement = "before",
   ) {
     return this._blockManager.insertBlocks(
       blocksToInsert,
diff --git a/packages/core/src/editor/managers/BlockManager.ts b/packages/core/src/editor/managers/BlockManager.ts
index f086444ecc..a33bfcab4b 100644
--- a/packages/core/src/editor/managers/BlockManager.ts
+++ b/packages/core/src/editor/managers/BlockManager.ts
@@ -1,4 +1,7 @@
-import { insertBlocks } from "../../api/blockManipulation/commands/insertBlocks/insertBlocks.js";
+import {
+  BlockPlacement,
+  insertBlocks,
+} from "../../api/blockManipulation/commands/insertBlocks/insertBlocks.js";
 import {
   moveBlocksDown,
   moveBlocksUp,
@@ -150,13 +153,13 @@ export class BlockManager<
    * error if the reference block could not be found.
    * @param blocksToInsert An array of partial blocks that should be inserted.
    * @param referenceBlock An identifier for an existing block, at which the new blocks should be inserted.
-   * @param placement Whether the blocks should be inserted just before, just after, or nested inside the
-   * `referenceBlock`.
+   * @param placement Where the blocks go relative to the `referenceBlock`: as its previous (`"before"`) or next
+   * (`"after"`) sibling, or nested inside it as its first (`"start"`) or last (`"end"`) children.
    */
   public insertBlocks(
     blocksToInsert: PartialBlock<BSchema, ISchema, SSchema>[],
     referenceBlock: BlockIdentifier,
-    placement: "before" | "after" = "before",
+    placement: BlockPlacement = "before",
   ) {
     return this.editor.transact((tr) =>
       insertBlocks(tr, blocksToInsert, referenceBlock, placement),
diff --git a/packages/core/src/editor/managers/ExtensionManager/extensions.ts b/packages/core/src/editor/managers/ExtensionManager/extensions.ts
index 853cca2493..83977b943d 100644
--- a/packages/core/src/editor/managers/ExtensionManager/extensions.ts
+++ b/packages/core/src/editor/managers/ExtensionManager/extensions.ts
@@ -39,6 +39,7 @@ import {
   UniqueID,
 } from "../../../extensions/tiptap-extensions/index.js";
 import { BlockContainer, BlockGroup, Doc } from "../../../pm-nodes/index.js";
+import { isContainerType } from "../../../schema/blocks/children.js";
 import type {
   BlockNoteEditor,
   BlockNoteEditorOptions,
@@ -62,7 +63,16 @@ export function getDefaultTiptapExtensions(
 
     UniqueID.configure({
       // everything from bnBlock group (nodes that represent a BlockNote block should have an id)
-      types: ["blockContainer", "columnList", "column"],
+      types: [
+        "blockContainer",
+        // Container block specs whose PM node is itself in the `bnBlock` group
+        // (column, columnList, callout, etc.) — i.e. the bnBlock node IS the
+        // block, so the id lives on its attrs rather than on a wrapping
+        // blockContainer.
+        ...Object.entries(editor.schema.blockSpecs)
+          .filter(([, spec]) => isContainerType((spec as any).config))
+          .map(([type]) => type),
+      ],
       setIdAttribute: options.setIdAttribute,
       isWithinEditor: editor.isWithinEditor,
     }),
@@ -130,6 +140,16 @@ export function getDefaultTiptapExtensions(
               }),
             ]
           : []),
+        // Nodes the block's node depends on but which aren't blocks
+        // themselves (a content-bearing container's content & children nodes).
+        ...("extraNodes" in blockSpec.implementation
+          ? (blockSpec.implementation.extraNodes as Node[]).map((node) =>
+              node.configure({
+                editor: editor,
+                domAttributes: options.domAttributes,
+              }),
+            )
+          : []),
       ];
     }),
     createCopyToClipboardExtension(editor),
diff --git a/packages/core/src/editor/managers/ExtensionManager/index.ts b/packages/core/src/editor/managers/ExtensionManager/index.ts
index 5cf6e74c1c..71167e8f5a 100644
--- a/packages/core/src/editor/managers/ExtensionManager/index.ts
+++ b/packages/core/src/editor/managers/ExtensionManager/index.ts
@@ -563,7 +563,7 @@ export class ExtensionManager {
                 const blockInfo = getBlockInfoFromSelection(tr);
 
                 if (
-                  !blockInfo.isBlockContainer ||
+                  !blockInfo.isWrappedBlock ||
                   this.editor.schema.blockSchema[blockInfo.blockNoteType]
                     ?.content !== "inline"
                 ) {
diff --git a/packages/core/src/editor/transformPasted.ts b/packages/core/src/editor/transformPasted.ts
index 4f0515df95..7b6b5b1d9e 100644
--- a/packages/core/src/editor/transformPasted.ts
+++ b/packages/core/src/editor/transformPasted.ts
@@ -213,9 +213,7 @@ function retypeLeadingParagraphForEmptyTarget(
   }
 
   const blockInfo = getBlockInfoFromSelection(view.state);
-  const target = blockInfo.isBlockContainer
-    ? blockInfo.blockContent.node
-    : null;
+  const target = blockInfo.isWrappedBlock ? blockInfo.blockContent.node : null;
   if (
     !target ||
     target.type.name === "paragraph" ||
@@ -275,7 +273,7 @@ function shouldApplyFix(fragment: Fragment, view: EditorView) {
       // for both paste and drop events. Drop events can potentially cause
       // issues as they don't always happen at the current selection.
       const blockInfo = getBlockInfoFromSelection(view.state);
-      if (blockInfo.isBlockContainer) {
+      if (blockInfo.isWrappedBlock) {
         const selectedBlockHasTableContent =
           blockInfo.blockContent.node.type.spec.content === "tableRow+";
 
diff --git a/packages/core/src/exporter/Exporter.ts b/packages/core/src/exporter/Exporter.ts
index 9c7a2650fd..fabb450c84 100644
--- a/packages/core/src/exporter/Exporter.ts
+++ b/packages/core/src/exporter/Exporter.ts
@@ -11,6 +11,7 @@ import {
   StyledText,
   Styles,
 } from "../schema/index.js";
+import { isContainerType } from "../schema/blocks/children.js";
 
 import type {
   BlockMapping,
@@ -60,15 +61,35 @@ export abstract class Exporter<
   RS,
   TS,
 > {
+  // Stored with erased generics: a generically-typed property would change
+  // the class's variance in B/I/S and break mapping inference at subclass
+  // construction sites (the schema param was previously inference-only).
+  private readonly blockNoteSchema: BlockNoteSchema<any, any, any>;
+
   public constructor(
-    _schema: BlockNoteSchema<B, I, S>, // only used for type inference
+    schema: BlockNoteSchema<B, I, S>,
     protected readonly mappings: {
       blockMapping: BlockMapping<B, I, S, RB, RI>;
       inlineContentMapping: InlineContentMapping<I, S, RI, TS>;
       styleMapping: StyleMapping<S, RS>;
     },
     public readonly options: ExporterOptions,
-  ) {}
+  ) {
+    this.blockNoteSchema = schema;
+  }
+
+  /**
+   * Whether a block type is a container block (declares `children`, e.g.
+   * `columnList`, `column`, or a custom callout). Container mappings own the
+   * placement of their children — exporters must not append the children
+   * after the container's own output.
+   */
+  public isContainerBlock(blockType: string): boolean {
+    const spec = (this.blockNoteSchema.blockSpecs as Record<string, any>)[
+      blockType
+    ];
+    return !!spec && isContainerType(spec.config);
+  }
 
   /**
    * The strings this exporter renders into the produced document - the
@@ -129,7 +150,9 @@ export abstract class Exporter<
     const mapping = this.mappings.blockMapping[block.type];
     if (!mapping) {
       throw new Error(
-        `Exporter is missing a block mapping for block type "${block.type}". If this block comes from a separate package, spread that package's exporter mappings into your blockMapping.`,
+        this.isContainerBlock(block.type)
+          ? `No mapping found for container block type "${block.type}" — container blocks require an explicit block mapping that places their children.`
+          : `Exporter is missing a block mapping for block type "${block.type}". If this block comes from a separate package, spread that package's exporter mappings into your blockMapping.`,
       );
     }
     return mapping(block, this, nestingLevel, numberedListIndex, children);
diff --git a/packages/core/src/extensions/SideMenu/SideMenu.ts b/packages/core/src/extensions/SideMenu/SideMenu.ts
index fddd2712e9..63dff6d346 100644
--- a/packages/core/src/extensions/SideMenu/SideMenu.ts
+++ b/packages/core/src/extensions/SideMenu/SideMenu.ts
@@ -20,8 +20,16 @@ import {
   InlineContentSchema,
   StyleSchema,
 } from "../../schema/index.js";
+import {
+  ContainerUIInfo,
+  getContainerUIInfo,
+} from "../../api/blockManipulation/containers/containerUI.js";
 import { getDraggableBlockFromElement } from "../getDraggableBlockFromElement.js";
 import { dragStart, unsetDragImage } from "./dragging.js";
+import {
+  getContainerChildAtCursor,
+  hasHorizontalContainerAncestor,
+} from "./sideMenuContainerGeometry.js";
 
 export type SideMenuState<
   BSchema extends BlockSchema,
@@ -37,7 +45,8 @@ const DISTANCE_TO_CONSIDER_EDITOR_BOUNDS = 250;
 function getBlockFromCoords(
   view: EditorView,
   coords: { left: number; top: number },
-  adjustForColumns = true,
+  containerUIInfo: ContainerUIInfo,
+  adjustForHorizontalContainers = true,
 ) {
   const elements = view.root.elementsFromPoint(coords.left, coords.top);
 
@@ -46,21 +55,28 @@ function getBlockFromCoords(
       // probably a ui overlay like formatting toolbar etc
       continue;
     }
-    if (adjustForColumns) {
-      const column = element.closest("[data-node-type=columnList]");
-      if (column) {
-        return getBlockFromCoords(
-          view,
-          {
-            // TODO can we do better than this?
-            left: coords.left + 50, // bit hacky, but if we're inside a column, offset x position to right to account for the width of sidemenu itself
-            top: coords.top,
-          },
-          false,
-        );
-      }
+    if (
+      adjustForHorizontalContainers &&
+      containerUIInfo.containerSelector &&
+      // Inside a container with side-by-side children (e.g. a columnList),
+      // the x position must be offset — the hovered coordinates land in the
+      // side menu's own gutter, which belongs to a different child. The
+      // horizontal container can be any ancestor (the element may sit inside
+      // a vertical child of it, like a block inside a column).
+      hasHorizontalContainerAncestor(element, containerUIInfo)
+    ) {
+      return getBlockFromCoords(
+        view,
+        {
+          // TODO can we do better than this?
+          left: coords.left + 50, // bit hacky, but if we're inside a column, offset x position to right to account for the width of sidemenu itself
+          top: coords.top,
+        },
+        containerUIInfo,
+        false,
+      );
     }
-    return getDraggableBlockFromElement(element, view);
+    return getDraggableBlockFromElement(element, view, containerUIInfo);
   }
   return undefined;
 }
@@ -71,6 +87,7 @@ function getBlockFromMousePos(
     y: number;
   },
   view: EditorView,
+  containerUIInfo: ContainerUIInfo,
 ): { node: HTMLElement; id: string } | undefined {
   // Editor itself may have padding or other styling which affects
   // size/position, so we get the boundingRect of the first child (i.e. the
@@ -94,7 +111,7 @@ function getBlockFromMousePos(
     top: mousePos.y,
   };
 
-  const referenceBlock = getBlockFromCoords(view, coords);
+  const referenceBlock = getBlockFromCoords(view, coords, containerUIInfo);
 
   if (!referenceBlock) {
     // could not find the reference block
@@ -109,15 +126,26 @@ function getBlockFromMousePos(
    * ```
    * Hovering at position x (left edge of BlockB) would return BlockA.
    * Instead, we check at position y (right edge of BlockA) to correctly identify BlockB.
+   * `elementsFromPoint` returns the deepest element at a point, so this single
+   * probe descends through any depth of regular nesting.
+   *
+   * When the reference block is a (draggable) container block, the probe is
+   * aimed at the direct child under the cursor instead of the container
+   * itself — the container's own padding can exceed the probe inset, which
+   * would keep resolving the container even though the cursor is aligned with
+   * one of its children (making the child's menu jump away as the cursor
+   * moves towards it).
    */
-  const referenceBlocksBoundingBox =
-    referenceBlock.node.getBoundingClientRect();
+  const probeTarget =
+    getContainerChildAtCursor(referenceBlock.node, mousePos, containerUIInfo) ??
+    referenceBlock.node;
   return getBlockFromCoords(
     view,
     {
-      left: referenceBlocksBoundingBox.right - 10,
+      left: probeTarget.getBoundingClientRect().right - 10,
       top: mousePos.y,
     },
+    containerUIInfo,
     false,
   );
 }
@@ -214,7 +242,11 @@ export class SideMenuView<
       return;
     }
 
-    const block = getBlockFromMousePos(this.mousePos, this.pmView);
+    const block = getBlockFromMousePos(
+      this.mousePos,
+      this.pmView,
+      getContainerUIInfo(this.editor),
+    );
 
     // Closes the menu if the mouse cursor is beyond the editor vertically.
     if (!block || !this.editor.isEditable) {
@@ -240,7 +272,15 @@ export class SideMenuView<
     // Shows or updates elements.
     if (this.editor.isEditable) {
       const blockContentBoundingBox = block.node.getBoundingClientRect();
-      const column = block.node.closest("[data-node-type=column]");
+      // The closest container ancestor (a column, callout, ...) — excluding
+      // the hovered block itself, which may be a draggable container. Blocks
+      // inside a container anchor the side menu to the container's block
+      // area rather than the editor's left edge, which would put the menu
+      // over unrelated content (or off-screen inside columns).
+      const containerUIInfo = getContainerUIInfo(this.editor);
+      const container = containerUIInfo.containerSelector
+        ? block.node.parentElement?.closest(containerUIInfo.containerSelector)
+        : undefined;
       const sideMenuBlock = this.editor.getBlock(
         this.hoveredBlock!.getAttribute("data-id")!,
       );
@@ -255,12 +295,16 @@ export class SideMenuView<
       this.state = {
         show: true,
         referencePos: new DOMRect(
-          column
-            ? // We take the first child as column elements have some default
-              // padding. This is a little weird since this child element will
-              // be the first block, but since it's always non-nested and we
-              // only take the x coordinate, it's ok.
-              column.firstElementChild!.getBoundingClientRect().x
+          container
+            ? // We anchor to the container's first block element (rather
+              // than the container itself, which may have padding or its own
+              // chrome around the block area). This is a little weird since
+              // this element is the first block, but since it's always
+              // non-nested and we only take the x coordinate, it's ok.
+              (
+                container.querySelector('[data-node-type="blockOuter"]') ??
+                container.firstElementChild!
+              ).getBoundingClientRect().x
             : (
                 this.pmView.dom.firstChild as HTMLElement
               ).getBoundingClientRect().x,
diff --git a/packages/core/src/extensions/SideMenu/sideMenuContainerGeometry.browser.test.ts b/packages/core/src/extensions/SideMenu/sideMenuContainerGeometry.browser.test.ts
new file mode 100644
index 0000000000..5bb52a71c9
--- /dev/null
+++ b/packages/core/src/extensions/SideMenu/sideMenuContainerGeometry.browser.test.ts
@@ -0,0 +1,267 @@
+import { afterEach, describe, expect, it } from "vite-plus/test";
+
+import type { ContainerUIInfo } from "../../api/blockManipulation/containers/containerUI.js";
+import {
+  getContainerChildAtCursor,
+  getDirectChildBlocks,
+  hasHorizontalContainerAncestor,
+  isHorizontalContainer,
+} from "./sideMenuContainerGeometry.js";
+
+// The DOM half of the side-menu container geometry: the `querySelectorAll` /
+// `closest` walks that find a container's direct child blocks, and the
+// live-layout claim the module exists for — that a container whose children
+// *happen* to sit side-by-side is recognised as horizontal without declaring
+// anything.
+//
+// Everything here is attached to the real document and laid out by the real
+// engine; nothing stubs `getBoundingClientRect`. The counterpart node suite
+// (`sideMenuContainerGeometry.test.ts`) covers the arithmetic these adapters
+// feed. A column list inside a real editor is covered end-to-end by
+// `tests/src/end-to-end/multicolumn/multicolumn.test.tsx`.
+
+let mounted: HTMLElement[] = [];
+
+afterEach(() => {
+  mounted.forEach((el) => el.remove());
+  mounted = [];
+});
+
+/** Attaches a tree to the document so the browser actually lays it out. */
+function mount<T extends HTMLElement>(el: T): T {
+  document.body.appendChild(el);
+  mounted.push(el);
+  return el;
+}
+
+function el(nodeType: string): HTMLElement {
+  const node = document.createElement("div");
+  node.setAttribute("data-node-type", nodeType);
+  return node;
+}
+
+/** The `blockOuter > blockContainer` chrome BlockNote renders around every
+ * regular block, with real text in it so it has a real height. */
+function regularChild(text = "block"): {
+  outer: HTMLElement;
+  blockContainer: HTMLElement;
+} {
+  const outer = el("blockOuter");
+  const blockContainer = el("blockContainer");
+  blockContainer.textContent = text;
+  outer.append(blockContainer);
+  return { outer, blockContainer };
+}
+
+function uiInfo(containerTypes: string[]): ContainerUIInfo {
+  const set = new Set(containerTypes);
+  return {
+    containerTypes: set,
+    draggableContainerTypes: set,
+    nonDraggableBlockTypes: new Set<string>(),
+    containerSelector: containerTypes.length
+      ? containerTypes.map((t) => `[data-node-type="${t}"]`).join(",")
+      : null,
+  };
+}
+
+/**
+ * A column list laid out the way the real one is: a flex row of two columns,
+ * each holding one block. Nothing declares "horizontal" — the browser puts the
+ * columns side by side and the module has to notice.
+ */
+function buildColumnList() {
+  const info = uiInfo(["columnList", "column"]);
+
+  const columnList = el("columnList");
+  columnList.style.display = "flex";
+  columnList.style.width = "400px";
+
+  const columnA = el("column");
+  const columnB = el("column");
+  for (const column of [columnA, columnB]) {
+    column.style.flex = "1";
+  }
+
+  const childA = regularChild("A");
+  const childB = regularChild("B");
+  columnA.append(childA.outer);
+  columnB.append(childB.outer);
+  columnList.append(columnA, columnB);
+  mount(columnList);
+
+  return { info, columnList, columnA, columnB, childA, childB };
+}
+
+/** A callout: an ordinary block-flow container, so its children stack. */
+function buildVerticalContainer() {
+  const info = uiInfo(["callout"]);
+
+  const callout = el("callout");
+  callout.style.width = "400px";
+  const first = regularChild("first");
+  const second = regularChild("second");
+  callout.append(first.outer, second.outer);
+  mount(callout);
+
+  return { info, callout, first, second };
+}
+
+describe("getDirectChildBlocks", () => {
+  it("returns direct child blocks, skipping nested grandchildren", () => {
+    const { info, columnList, columnA, columnB } = buildColumnList();
+
+    // The blocks inside each column must not come back as the list's own
+    // children — the `closest` check is what stops the walk one level down.
+    expect(getDirectChildBlocks(columnList, info)).toEqual([columnA, columnB]);
+  });
+
+  it("sees through blockOuter wrappers to the blockContainer child", () => {
+    const { info, columnA, childA } = buildColumnList();
+
+    // The column's own direct child is the wrapped blockContainer, not the
+    // blockOuter chrome (which isn't a block in the selector's sense).
+    expect(getDirectChildBlocks(columnA, info)).toEqual([
+      childA.blockContainer,
+    ]);
+  });
+
+  it("returns nothing for a container with no block children", () => {
+    const info = uiInfo(["callout"]);
+    const empty = mount(el("callout"));
+
+    expect(getDirectChildBlocks(empty, info)).toEqual([]);
+  });
+});
+
+describe("isHorizontalContainer", () => {
+  it("recognises a real flex row as horizontal", () => {
+    const { info, columnList, columnA, columnB } = buildColumnList();
+
+    // The claim the module exists for, asserted against real layout: nothing
+    // declares the column list horizontal, and no rect is stubbed.
+    expect(isHorizontalContainer(columnList, info)).toBe(true);
+
+    // Stated as geometry too, so a failure says whether the layout or the
+    // detection is what broke.
+    const a = columnA.getBoundingClientRect();
+    const b = columnB.getBoundingClientRect();
+    expect(a.width).toBeGreaterThan(0);
+    expect(b.left).toBeGreaterThanOrEqual(a.right - 1);
+    expect(a.top).toBe(b.top);
+  });
+
+  it("is false for a container whose children stack", () => {
+    const { info, callout, first, second } = buildVerticalContainer();
+
+    expect(isHorizontalContainer(callout, info)).toBe(false);
+
+    const a = first.blockContainer.getBoundingClientRect();
+    const b = second.blockContainer.getBoundingClientRect();
+    expect(a.height).toBeGreaterThan(0);
+    expect(b.top).toBeGreaterThanOrEqual(a.bottom);
+  });
+
+  it("is false for a column holding a single block", () => {
+    const { info, columnA } = buildColumnList();
+
+    expect(isHorizontalContainer(columnA, info)).toBe(false);
+  });
+});
+
+describe("hasHorizontalContainerAncestor", () => {
+  it("is true for a block nested inside a column of a column list", () => {
+    const { info, childA } = buildColumnList();
+
+    // The block sits inside a (vertical) column, whose parent column list is
+    // the horizontal one — the walk must climb past the column.
+    expect(hasHorizontalContainerAncestor(childA.blockContainer, info)).toBe(
+      true,
+    );
+  });
+
+  it("is false for a block inside a purely vertical container", () => {
+    const { info, first } = buildVerticalContainer();
+
+    expect(hasHorizontalContainerAncestor(first.blockContainer, info)).toBe(
+      false,
+    );
+  });
+
+  it("is false when there is no container ancestor", () => {
+    const info = uiInfo(["columnList", "column"]);
+    const loose = regularChild();
+    mount(loose.outer);
+
+    expect(hasHorizontalContainerAncestor(loose.blockContainer, info)).toBe(
+      false,
+    );
+  });
+
+  it("is false when the schema declares no containers", () => {
+    const { childA } = buildColumnList();
+
+    expect(
+      hasHorizontalContainerAncestor(childA.blockContainer, uiInfo([])),
+    ).toBe(false);
+  });
+});
+
+describe("getContainerChildAtCursor", () => {
+  it("returns undefined for a non-container element", () => {
+    const { info, childA } = buildColumnList();
+
+    expect(
+      getContainerChildAtCursor(childA.blockContainer, { x: 10, y: 10 }, info),
+    ).toBeUndefined();
+  });
+
+  it("resolves the hovered column of a real row", () => {
+    const { info, columnList, columnA, columnB } = buildColumnList();
+    const b = columnB.getBoundingClientRect();
+
+    expect(
+      getContainerChildAtCursor(
+        columnList,
+        { x: b.left + b.width / 2, y: b.top + b.height / 2 },
+        info,
+      ),
+    ).toBe(columnB);
+
+    const a = columnA.getBoundingClientRect();
+    expect(
+      getContainerChildAtCursor(
+        columnList,
+        { x: a.left + a.width / 2, y: a.top + a.height / 2 },
+        info,
+      ),
+    ).toBe(columnA);
+  });
+
+  it("falls back to the block on that row when x is in the gutter", () => {
+    const { info, callout, first } = buildVerticalContainer();
+    const rect = first.blockContainer.getBoundingClientRect();
+
+    // The cursor's y is in the first block's band but its x is left of the
+    // container entirely — where the side menu renders.
+    expect(
+      getContainerChildAtCursor(
+        callout,
+        { x: rect.left - 20, y: rect.top + rect.height / 2 },
+        info,
+      ),
+    ).toBe(first.blockContainer);
+  });
+
+  it("returns undefined when the cursor is below all children", () => {
+    const { info, callout } = buildVerticalContainer();
+
+    expect(
+      getContainerChildAtCursor(
+        callout,
+        { x: 10, y: callout.getBoundingClientRect().bottom + 500 },
+        info,
+      ),
+    ).toBeUndefined();
+  });
+});
diff --git a/packages/core/src/extensions/SideMenu/sideMenuContainerGeometry.test.ts b/packages/core/src/extensions/SideMenu/sideMenuContainerGeometry.test.ts
new file mode 100644
index 0000000000..9cbdfcdbd8
--- /dev/null
+++ b/packages/core/src/extensions/SideMenu/sideMenuContainerGeometry.test.ts
@@ -0,0 +1,112 @@
+// @vitest-environment node
+import { describe, expect, it } from "vite-plus/test";
+
+import {
+  rectIndexAtCursor,
+  rectsAreSideBySide,
+  type BlockRect,
+} from "./sideMenuContainerGeometry.js";
+
+// The arithmetic half of the side-menu container geometry: pure functions over
+// rects, so there is nothing to stub and no DOM to build. These used to be
+// tested through the DOM adapters with `getBoundingClientRect` monkey-patched
+// onto detached elements — which faked the one input the module exists to read.
+// The adapters (and the claim that a real column list really does lay its
+// children out side-by-side) are covered against real layout in
+// `sideMenuContainerGeometry.browser.test.ts`.
+
+const rect = (
+  top: number,
+  bottom: number,
+  left: number,
+  right: number,
+): BlockRect => ({ top, bottom, left, right });
+
+// Two columns of a column list: same vertical band, adjacent horizontally.
+const SIDE_BY_SIDE = [rect(0, 100, 0, 100), rect(0, 100, 100, 200)];
+// Two blocks of a callout: same horizontal band, stacked vertically with a gap
+// between them (the abutting, gap-free case is its own test below).
+const STACKED = [rect(0, 40, 0, 200), rect(50, 90, 0, 200)];
+
+describe("rectsAreSideBySide", () => {
+  it("is true when two rects overlap vertically", () => {
+    expect(rectsAreSideBySide(SIDE_BY_SIDE)).toBe(true);
+  });
+
+  it("is false when rects are stacked", () => {
+    expect(rectsAreSideBySide(STACKED)).toBe(false);
+  });
+
+  it("is false for a single rect", () => {
+    expect(rectsAreSideBySide([rect(0, 100, 0, 100)])).toBe(false);
+  });
+
+  it("is false for no rects at all", () => {
+    expect(rectsAreSideBySide([])).toBe(false);
+  });
+
+  it("treats abutting (non-overlapping) rects as stacked", () => {
+    // The second rect's top exactly meets the first's bottom — a stack with no
+    // gap must not be misread as a row.
+    expect(
+      rectsAreSideBySide([rect(0, 40, 0, 200), rect(40, 80, 0, 200)]),
+    ).toBe(false);
+  });
+
+  it("finds an overlapping pair that isn't the first two", () => {
+    // The loop is over every pair, not just neighbours: a column list whose
+    // first two children happen to be stacked is still a row.
+    expect(
+      rectsAreSideBySide([
+        rect(0, 40, 0, 100),
+        rect(40, 80, 0, 100),
+        rect(40, 80, 100, 200),
+      ]),
+    ).toBe(true);
+  });
+
+  it("counts even a one-pixel vertical overlap", () => {
+    expect(
+      rectsAreSideBySide([rect(0, 41, 0, 100), rect(40, 80, 0, 100)]),
+    ).toBe(true);
+  });
+});
+
+describe("rectIndexAtCursor", () => {
+  it("returns the rect whose x range contains the cursor (side-by-side)", () => {
+    // Both rects share the y range, so only x distinguishes them. x=150 lands
+    // in the second: the vertical-only fallback recorded for the first must not
+    // win over an x match found later in the list. This is what makes hovering
+    // the second column of a row resolve to it rather than to its neighbour.
+    expect(rectIndexAtCursor(SIDE_BY_SIDE, { x: 150, y: 50 })).toBe(1);
+  });
+
+  it("prefers the x match over the first vertical match", () => {
+    // The mirror of the above: x=10 is within the first rect.
+    expect(rectIndexAtCursor(SIDE_BY_SIDE, { x: 10, y: 50 })).toBe(0);
+  });
+
+  it("falls back to the first vertical match when x is in the gutter", () => {
+    // The cursor's y is in the first block's band but its x is left of it (the
+    // side-menu gutter). The first vertical match wins.
+    expect(rectIndexAtCursor(STACKED, { x: -20, y: 20 })).toBe(0);
+  });
+
+  it("returns undefined when the cursor is below every rect", () => {
+    expect(rectIndexAtCursor(STACKED, { x: 10, y: 999 })).toBeUndefined();
+  });
+
+  it("returns undefined when the cursor is above every rect", () => {
+    expect(rectIndexAtCursor(STACKED, { x: 10, y: -999 })).toBeUndefined();
+  });
+
+  it("returns undefined for no rects at all", () => {
+    expect(rectIndexAtCursor([], { x: 10, y: 10 })).toBeUndefined();
+  });
+
+  it("includes the rect edges", () => {
+    const single = [rect(0, 40, 0, 200)];
+    expect(rectIndexAtCursor(single, { x: 0, y: 0 })).toBe(0);
+    expect(rectIndexAtCursor(single, { x: 200, y: 40 })).toBe(0);
+  });
+});
diff --git a/packages/core/src/extensions/SideMenu/sideMenuContainerGeometry.ts b/packages/core/src/extensions/SideMenu/sideMenuContainerGeometry.ts
new file mode 100644
index 0000000000..87f13f9c13
--- /dev/null
+++ b/packages/core/src/extensions/SideMenu/sideMenuContainerGeometry.ts
@@ -0,0 +1,107 @@
+import type { ContainerUIInfo } from "../../api/blockManipulation/containers/containerUI.js";
+
+function containerChildSelector(containerUIInfo: ContainerUIInfo): string {
+  return containerUIInfo.containerSelector
+    ? `[data-node-type="blockContainer"],${containerUIInfo.containerSelector}`
+    : `[data-node-type="blockContainer"]`;
+}
+
+export function getDirectChildBlocks(
+  container: Element,
+  containerUIInfo: ContainerUIInfo,
+): Element[] {
+  const childSelector = containerChildSelector(containerUIInfo);
+
+  const children: Element[] = [];
+  for (const child of container.querySelectorAll(childSelector)) {
+    if (child.parentElement?.closest(childSelector) === container) {
+      children.push(child);
+    }
+  }
+  return children;
+}
+
+export type BlockRect = {
+  top: number;
+  bottom: number;
+  left: number;
+  right: number;
+};
+
+export function rectsAreSideBySide(rects: BlockRect[]): boolean {
+  for (let i = 0; i < rects.length; i++) {
+    for (let j = i + 1; j < rects.length; j++) {
+      if (rects[i].top < rects[j].bottom && rects[j].top < rects[i].bottom) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+// X-match wins over y-only match (disambiguates side-by-side children).
+export function rectIndexAtCursor(
+  rects: BlockRect[],
+  mousePos: { x: number; y: number },
+): number | undefined {
+  let verticalMatch: number | undefined = undefined;
+  for (let i = 0; i < rects.length; i++) {
+    const rect = rects[i];
+    if (mousePos.y < rect.top || mousePos.y > rect.bottom) {
+      continue;
+    }
+    if (mousePos.x >= rect.left && mousePos.x <= rect.right) {
+      return i;
+    }
+    verticalMatch = verticalMatch ?? i;
+  }
+  return verticalMatch;
+}
+
+export function isHorizontalContainer(
+  container: Element,
+  containerUIInfo: ContainerUIInfo,
+): boolean {
+  return rectsAreSideBySide(
+    getDirectChildBlocks(container, containerUIInfo).map((child) =>
+      child.getBoundingClientRect(),
+    ),
+  );
+}
+
+export function hasHorizontalContainerAncestor(
+  element: Element,
+  containerUIInfo: ContainerUIInfo,
+): boolean {
+  if (!containerUIInfo.containerSelector) {
+    return false;
+  }
+  let container = element.closest(containerUIInfo.containerSelector);
+  while (container) {
+    if (isHorizontalContainer(container, containerUIInfo)) {
+      return true;
+    }
+    container =
+      container.parentElement?.closest(containerUIInfo.containerSelector) ??
+      null;
+  }
+  return false;
+}
+
+export function getContainerChildAtCursor(
+  element: Element,
+  mousePos: { x: number; y: number },
+  containerUIInfo: ContainerUIInfo,
+): Element | undefined {
+  const nodeType = element.getAttribute("data-node-type");
+  if (!nodeType || !containerUIInfo.containerTypes.has(nodeType)) {
+    return undefined;
+  }
+
+  const children = getDirectChildBlocks(element, containerUIInfo);
+  const index = rectIndexAtCursor(
+    children.map((child) => child.getBoundingClientRect()),
+    mousePos,
+  );
+  return index === undefined ? undefined : children[index];
+}
diff --git a/packages/core/src/extensions/getDraggableBlockFromElement.browser.test.ts b/packages/core/src/extensions/getDraggableBlockFromElement.browser.test.ts
new file mode 100644
index 0000000000..97c775267d
--- /dev/null
+++ b/packages/core/src/extensions/getDraggableBlockFromElement.browser.test.ts
@@ -0,0 +1,111 @@
+import { describe, expect, it } from "vite-plus/test";
+
+import { getDraggableBlockFromElement } from "./getDraggableBlockFromElement.js";
+
+// These are pure DOM walks (`closest`/`querySelector` over the block chrome),
+// so we build detached trees rather than booting an editor. Only `view.dom` is
+// read, as the stop condition for the upward walk. No layout is involved, but
+// the unit under test *is* the DOM API surface, so it runs against a real
+// browser engine rather than jsdom's re-implementation of it.
+
+/** Builds the `blockOuter > blockContainer > blockContent` chrome BlockNote
+ * renders around every regular block. */
+function regularBlock(
+  id: string,
+  contentType: string,
+): { outer: HTMLElement; blockContainer: HTMLElement; content: HTMLElement } {
+  const outer = document.createElement("div");
+  outer.setAttribute("data-node-type", "blockOuter");
+
+  const blockContainer = document.createElement("div");
+  blockContainer.setAttribute("data-node-type", "blockContainer");
+  blockContainer.setAttribute("data-id", id);
+
+  const content = document.createElement("div");
+  content.setAttribute("data-content-type", contentType);
+
+  blockContainer.append(content);
+  outer.append(blockContainer);
+  return { outer, blockContainer, content };
+}
+
+/** Nests `child` under `parent` in a `blockGroup`, as list nesting does. */
+function nest(parent: HTMLElement, child: HTMLElement) {
+  const group = document.createElement("div");
+  group.setAttribute("data-node-type", "blockGroup");
+  group.append(child);
+  parent.append(group);
+}
+
+function viewWith(root: HTMLElement) {
+  const dom = document.createElement("div");
+  dom.append(root);
+  return { dom };
+}
+
+describe("getDraggableBlockFromElement", () => {
+  it("returns the block container for a regular block", () => {
+    const { outer, blockContainer, content } = regularBlock("a", "paragraph");
+
+    expect(getDraggableBlockFromElement(content, viewWith(outer))).toEqual({
+      node: blockContainer,
+      id: "a",
+    });
+  });
+
+  it("skips a block whose type opts out of dragging", () => {
+    const { outer, content } = regularBlock("a", "lockedBlock");
+
+    expect(
+      getDraggableBlockFromElement(content, viewWith(outer), {
+        nonDraggableBlockTypes: new Set(["lockedBlock"]),
+      }),
+    ).toBeUndefined();
+  });
+
+  it("falls through to the nearest draggable ancestor", () => {
+    const parent = regularBlock("parent", "paragraph");
+    const child = regularBlock("child", "lockedBlock");
+    nest(parent.blockContainer, child.outer);
+
+    // Dragging from inside the locked child should hand back the parent's
+    // handle rather than no handle at all.
+    expect(
+      getDraggableBlockFromElement(child.content, viewWith(parent.outer), {
+        nonDraggableBlockTypes: new Set(["lockedBlock"]),
+      }),
+    ).toEqual({ node: parent.blockContainer, id: "parent" });
+  });
+
+  it("reads the block's own content type, not a nested block's", () => {
+    const parent = regularBlock("parent", "lockedBlock");
+    const child = regularBlock("child", "paragraph");
+    nest(parent.blockContainer, child.outer);
+
+    // `parent`'s own content element precedes the nested `blockGroup`, so the
+    // first `[data-content-type]` match inside it must be "lockedBlock".
+    expect(
+      getDraggableBlockFromElement(parent.content, viewWith(parent.outer), {
+        nonDraggableBlockTypes: new Set(["lockedBlock"]),
+      }),
+    ).toBeUndefined();
+  });
+
+  it("returns a container block only when its type is draggable", () => {
+    const column = document.createElement("div");
+    column.setAttribute("data-node-type", "column");
+    column.setAttribute("data-id", "col");
+
+    expect(
+      getDraggableBlockFromElement(column, viewWith(column), {
+        draggableContainerTypes: new Set(["columnList"]),
+      }),
+    ).toBeUndefined();
+
+    expect(
+      getDraggableBlockFromElement(column, viewWith(column), {
+        draggableContainerTypes: new Set(["column"]),
+      }),
+    ).toEqual({ node: column, id: "col" });
+  });
+});
diff --git a/packages/core/src/extensions/getDraggableBlockFromElement.ts b/packages/core/src/extensions/getDraggableBlockFromElement.ts
index abc6bd2906..188f3d6503 100644
--- a/packages/core/src/extensions/getDraggableBlockFromElement.ts
+++ b/packages/core/src/extensions/getDraggableBlockFromElement.ts
@@ -1,18 +1,59 @@
 import { EditorView } from "prosemirror-view";
 
+const EMPTY_SET: ReadonlySet<string> = new Set();
+
+/**
+ * Walks up from `element` to the closest element that can host a side-menu
+ * drag handle. Both sets are derived from each spec's `meta.draggable` (see
+ * `getContainerUIInfo`); a block that opts out is skipped, so the handle falls
+ * through to the nearest draggable ancestor rather than disappearing.
+ */
 export function getDraggableBlockFromElement(
   element: Element,
-  view: EditorView,
+  // Only `dom` is read — the stop condition for the upward walk.
+  view: Pick<EditorView, "dom">,
+  types: {
+    draggableContainerTypes?: ReadonlySet<string>;
+    nonDraggableBlockTypes?: ReadonlySet<string>;
+  } = {},
 ) {
+  const draggableContainerTypes = types.draggableContainerTypes ?? EMPTY_SET;
+  const nonDraggableBlockTypes = types.nonDraggableBlockTypes ?? EMPTY_SET;
+
+  const isDraggable = (el: Element) => {
+    const nodeType = el.getAttribute?.("data-node-type");
+
+    if (nodeType === "blockContainer") {
+      if (nonDraggableBlockTypes.size === 0) {
+        return true;
+      }
+      // Every regular block shares the `blockContainer` node, so its actual
+      // block type only shows up on its content element. That element comes
+      // before any nested `blockGroup`, so the first match in document order
+      // is this block's own content rather than a descendant's.
+      const contentType = el
+        .querySelector("[data-content-type]")
+        ?.getAttribute("data-content-type");
+
+      return !contentType || !nonDraggableBlockTypes.has(contentType);
+    }
+
+    return (
+      nodeType !== null &&
+      nodeType !== undefined &&
+      draggableContainerTypes.has(nodeType)
+    );
+  };
+
   while (
     element &&
     element.parentElement &&
     element.parentElement !== view.dom &&
-    element.getAttribute?.("data-node-type") !== "blockContainer"
+    !isDraggable(element)
   ) {
     element = element.parentElement;
   }
-  if (element.getAttribute?.("data-node-type") !== "blockContainer") {
+  if (!isDraggable(element)) {
     return undefined;
   }
   return { node: element as HTMLElement, id: element.getAttribute("data-id")! };
diff --git a/packages/core/src/extensions/tiptap-extensions/KeyboardShortcuts/KeyboardShortcutsExtension.ts b/packages/core/src/extensions/tiptap-extensions/KeyboardShortcuts/KeyboardShortcutsExtension.ts
index 4d1758094a..b50d57aef9 100644
--- a/packages/core/src/extensions/tiptap-extensions/KeyboardShortcuts/KeyboardShortcutsExtension.ts
+++ b/packages/core/src/extensions/tiptap-extensions/KeyboardShortcuts/KeyboardShortcutsExtension.ts
@@ -8,13 +8,28 @@ import {
   getParentBlockInfo,
   getPrevBlockInfo,
   mergeBlocksCommand,
+  mergeIntoContainerContent,
 } from "../../../api/blockManipulation/commands/mergeBlocks/mergeBlocks.js";
 import {
   liftItem,
   nestBlock,
   unnestBlock,
 } from "../../../api/blockManipulation/commands/nestBlock/nestBlock.js";
-import { fixColumnList } from "../../../api/blockManipulation/commands/replaceBlocks/util/fixColumnList.js";
+import {
+  fixContainersById,
+  isContainerNode,
+} from "../../../api/blockManipulation/containers/fixContainer.js";
+import {
+  ascendToInsertablePos,
+  descendToLastInsertionPos,
+  getAncestorContainers,
+  getFirstLeafBlock,
+} from "../../../api/blockManipulation/containers/containerNav.js";
+import {
+  getChildrenConfig,
+  isContentContainerNode,
+  resolveChildren,
+} from "../../../schema/blocks/children.js";
 import { splitBlockCommand } from "../../../api/blockManipulation/commands/splitBlock/splitBlock.js";
 import { updateBlockCommand } from "../../../api/blockManipulation/commands/updateBlock/updateBlock.js";
 import {
@@ -45,7 +60,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
         () =>
           commands.command(({ state }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -69,7 +84,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
         () =>
           commands.command(({ state, tr }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
             const { blockContent } = blockInfo;
@@ -92,7 +107,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
         () =>
           commands.command(({ state }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
             const { bnBlock: blockContainer, blockContent } = blockInfo;
@@ -106,7 +121,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
             // return early here.
             if (
               !prevBlockInfo ||
-              !prevBlockInfo.isBlockContainer ||
+              !prevBlockInfo.isWrappedBlock ||
               prevBlockInfo.blockContent.node.type.spec.content !== "inline*"
             ) {
               return false;
@@ -127,12 +142,14 @@ export const KeyboardShortcutsExtension = Extension.create<{
 
             return false;
           }),
-        // If the previous block is a columnList, moves the current block to
-        // the end of the last column in it.
+        // If the previous block is a container (e.g. a columnList or a
+        // callout), moves the current block to its deepest trailing insertion
+        // slot — descending through nested containers, e.g. to the end of the
+        // last column.
         () =>
           commands.command(({ state, tr, dispatch }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -146,21 +163,27 @@ export const KeyboardShortcutsExtension = Extension.create<{
               state.doc,
               blockInfo.bnBlock.beforePos,
             );
-            if (!prevBlockInfo || prevBlockInfo.isBlockContainer) {
+            if (!prevBlockInfo || prevBlockInfo.isWrappedBlock) {
               return false;
             }
 
-            if (dispatch) {
-              const columnAfterPos = prevBlockInfo.bnBlock.afterPos - 1;
-              const $blockAfterPos = tr.doc.resolve(columnAfterPos - 1);
+            const insertionPos = descendToLastInsertionPos(
+              prevBlockInfo.bnBlock.node,
+              prevBlockInfo.bnBlock.beforePos,
+              state.schema.nodes["blockContainer"],
+            );
+            if (insertionPos === null) {
+              return false;
+            }
 
+            if (dispatch) {
               tr.delete(
                 blockInfo.bnBlock.beforePos,
                 blockInfo.bnBlock.afterPos,
               );
-              tr.insert($blockAfterPos.pos, blockInfo.bnBlock.node);
+              tr.insert(insertionPos, blockInfo.bnBlock.node);
               tr.setSelection(
-                TextSelection.near(tr.doc.resolve($blockAfterPos.pos + 1)),
+                TextSelection.near(tr.doc.resolve(insertionPos + 1)),
               );
 
               return true;
@@ -168,13 +191,55 @@ export const KeyboardShortcutsExtension = Extension.create<{
 
             return false;
           }),
-        // If the block is the first in a column, moves it to the end of the
-        // previous column. If there is no previous column, moves it above the
-        // columnList.
+        // If the block is the first child of a container that has its own
+        // content, merges it into that content — the mirror of the Delete
+        // case. A *pure* container has nothing to merge into, so it falls
+        // through to the "move it out" branch below, as before.
+        () =>
+          commands.command(({ state, dispatch }) => {
+            const blockInfo = getBlockInfoFromSelection(state);
+            if (!blockInfo.isWrappedBlock) {
+              return false;
+            }
+
+            const selectionAtBlockStart =
+              state.selection.from === blockInfo.blockContent.beforePos + 1;
+            if (!selectionAtBlockStart || !state.selection.empty) {
+              return false;
+            }
+
+            // Only the container's first child.
+            if (state.doc.resolve(blockInfo.bnBlock.beforePos).nodeBefore) {
+              return false;
+            }
+
+            const parentInfo = getParentBlockInfo(
+              state.doc,
+              blockInfo.bnBlock.beforePos,
+            );
+            if (
+              !parentInfo ||
+              !isContentContainerNode(parentInfo.bnBlock.node)
+            ) {
+              return false;
+            }
+
+            return mergeIntoContainerContent(
+              state,
+              dispatch,
+              parentInfo,
+              blockInfo,
+            );
+          }),
+        // If the block is the first in a container (e.g. a column or a
+        // callout), moves it out: to the end of the previous sibling
+        // container if there is one (e.g. the previous column), otherwise to
+        // just before the closest enclosing boundary that accepts it (e.g.
+        // above the columnList / callout).
         () =>
           commands.command(({ state, tr, dispatch }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -192,32 +257,55 @@ export const KeyboardShortcutsExtension = Extension.create<{
             }
 
             const parentBlock = $pos.node();
-            if (parentBlock.type.name !== "column") {
+            if (!isContainerNode(parentBlock.type)) {
               return false;
             }
 
-            const $blockPos = tr.doc.resolve(blockInfo.bnBlock.beforePos);
-            const $columnPos = tr.doc.resolve($blockPos.before());
-            const columnListPos = $columnPos.before();
+            const blockContainerType = state.schema.nodes["blockContainer"];
+            const containerBeforePos = $pos.before();
+            const $containerPos = tr.doc.resolve(containerBeforePos);
+
+            // A previous sibling inside an enclosing container (e.g. the
+            // previous column) is a target to descend into. A sibling at a
+            // regular block position is not — there the block moves out to
+            // before the container instead.
+            const prevSibling =
+              isContainerNode($containerPos.node().type) &&
+              $containerPos.nodeBefore &&
+              isContainerNode($containerPos.nodeBefore.type)
+                ? $containerPos.nodeBefore
+                : null;
+
+            const insertionPos = prevSibling
+              ? descendToLastInsertionPos(
+                  prevSibling,
+                  containerBeforePos - prevSibling.nodeSize,
+                  blockContainerType,
+                )
+              : ascendToInsertablePos(
+                  tr.doc,
+                  containerBeforePos,
+                  blockContainerType,
+                );
+            if (insertionPos === null) {
+              return false;
+            }
 
             if (dispatch) {
+              const containersToFix = getAncestorContainers(
+                tr.doc,
+                blockInfo.bnBlock.beforePos,
+              );
+
               tr.delete(
                 blockInfo.bnBlock.beforePos,
                 blockInfo.bnBlock.afterPos,
               );
-              fixColumnList(tr, columnListPos);
-
-              if ($columnPos.pos === columnListPos + 1) {
-                tr.insert(columnListPos, blockInfo.bnBlock.node);
-                tr.setSelection(
-                  TextSelection.near(tr.doc.resolve(columnListPos)),
-                );
-              } else {
-                tr.insert($columnPos.pos - 1, blockInfo.bnBlock.node);
-                tr.setSelection(
-                  TextSelection.near(tr.doc.resolve($columnPos.pos)),
-                );
-              }
+              tr.insert(insertionPos, blockInfo.bnBlock.node);
+              fixContainersById(tr, containersToFix);
+              tr.setSelection(
+                TextSelection.near(tr.doc.resolve(insertionPos + 1)),
+              );
             }
 
             return true;
@@ -227,7 +315,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
         () =>
           commands.command(({ state }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -247,12 +335,12 @@ export const KeyboardShortcutsExtension = Extension.create<{
                 state.doc,
                 prevBlockInfo,
               );
-              if (!bottomNestedPrevBlockInfo.isBlockContainer) {
+              if (!bottomNestedPrevBlockInfo.isWrappedBlock) {
                 return false;
               }
               if (
                 !bottomNestedPrevBlockInfo ||
-                !bottomNestedPrevBlockInfo.isBlockContainer
+                !bottomNestedPrevBlockInfo.isWrappedBlock
               ) {
                 return false;
               }
@@ -313,7 +401,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
           commands.command(({ state }) => {
             const blockInfo = getBlockInfoFromSelection(state);
 
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -332,7 +420,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
                 prevBlockInfo,
               );
 
-              if (!bottomBlock.isBlockContainer) {
+              if (!bottomBlock.isWrappedBlock) {
                 return false;
               }
 
@@ -375,11 +463,17 @@ export const KeyboardShortcutsExtension = Extension.create<{
         () =>
           commands.command(({ state }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer || !blockInfo.childContainer) {
+            if (!blockInfo.isWrappedBlock || !blockInfo.childContainer) {
               return false;
             }
             const { blockContent, childContainer } = blockInfo;
 
+            // A container allowed to hold no children still has a child
+            // container node, but no first child to pull anything out of.
+            if (childContainer.node.childCount === 0) {
+              return false;
+            }
+
             const selectionAtBlockEnd =
               state.selection.from === blockContent.afterPos - 1;
             const selectionEmpty = state.selection.empty;
@@ -387,7 +481,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
             const firstChildBlockInfo = getBlockInfoFromResolvedPos(
               state.doc.resolve(childContainer.beforePos + 1),
             );
-            if (!firstChildBlockInfo.isBlockContainer) {
+            if (!firstChildBlockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -408,8 +502,12 @@ export const KeyboardShortcutsExtension = Extension.create<{
                       Fragment.empty,
                   )
                   .deleteRange(
-                    // Deletes whole child container if there's only one child.
-                    childContainer.node.childCount === 1
+                    // Deletes whole child container if there's only one child
+                    // — but a container with its own content always has one
+                    // (its children node is part of its content expression),
+                    // so there only the child itself goes.
+                    childContainer.node.childCount === 1 &&
+                      !isContentContainerNode(blockInfo.bnBlock.node)
                       ? {
                           from: childContainer.beforePos,
                           to: childContainer.afterPos,
@@ -440,7 +538,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
         () =>
           commands.command(({ state }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
             const { bnBlock: blockContainer, blockContent } = blockInfo;
@@ -449,7 +547,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
               state.doc,
               blockInfo.bnBlock.beforePos,
             );
-            if (!nextBlockInfo || !nextBlockInfo.isBlockContainer) {
+            if (!nextBlockInfo || !nextBlockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -468,12 +566,12 @@ export const KeyboardShortcutsExtension = Extension.create<{
 
             return false;
           }),
-        // If the next block is a columnList, moves the first block from its
-        // first column to after the current block.
+        // If the next block is a container (e.g. a columnList or a callout),
+        // moves its first leaf block out, to after the current block.
         () =>
           commands.command(({ state, tr, dispatch }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -487,22 +585,32 @@ export const KeyboardShortcutsExtension = Extension.create<{
               state.doc,
               blockInfo.bnBlock.beforePos,
             );
-            if (!nextBlockInfo || nextBlockInfo.isBlockContainer) {
+            if (!nextBlockInfo || nextBlockInfo.isWrappedBlock) {
+              return false;
+            }
+
+            const firstLeaf = getFirstLeafBlock(
+              nextBlockInfo.bnBlock.node,
+              nextBlockInfo.bnBlock.beforePos,
+            );
+            if (!firstLeaf) {
               return false;
             }
 
             if (dispatch) {
-              const columnBeforePos = nextBlockInfo.bnBlock.beforePos + 1;
-              const $blockBeforePos = tr.doc.resolve(columnBeforePos + 1);
+              const containersToFix = getAncestorContainers(
+                tr.doc,
+                firstLeaf.beforePos,
+              );
 
               tr.delete(
-                $blockBeforePos.pos,
-                $blockBeforePos.pos + $blockBeforePos.nodeAfter!.nodeSize,
+                firstLeaf.beforePos,
+                firstLeaf.beforePos + firstLeaf.node.nodeSize,
               );
-              fixColumnList(tr, nextBlockInfo.bnBlock.beforePos);
-              tr.insert(blockInfo.bnBlock.afterPos, $blockBeforePos.nodeAfter!);
+              tr.insert(blockInfo.bnBlock.afterPos, firstLeaf.node);
+              fixContainersById(tr, containersToFix);
               tr.setSelection(
-                TextSelection.near(tr.doc.resolve($blockBeforePos.pos)),
+                TextSelection.near(tr.doc.resolve(firstLeaf.beforePos)),
               );
 
               return true;
@@ -510,13 +618,14 @@ export const KeyboardShortcutsExtension = Extension.create<{
 
             return false;
           }),
-        // If the block is the last in a column, moves it to the start of the
-        // next column. If there is no next column, moves it below the
-        // columnList.
+        // If the block is the last in a container (e.g. a column or a
+        // callout), moves the next block — the first leaf of the next sibling
+        // container, or the block following the enclosing containers — to
+        // after it.
         () =>
           commands.command(({ state, tr, dispatch }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -534,36 +643,49 @@ export const KeyboardShortcutsExtension = Extension.create<{
             }
 
             const parentBlock = $pos.node();
-            if (parentBlock.type.name !== "column") {
+            if (!isContainerNode(parentBlock.type)) {
               return false;
             }
 
-            const $blockEndPos = tr.doc.resolve(blockInfo.bnBlock.afterPos);
-            const $columnEndPos = tr.doc.resolve($blockEndPos.after());
-            const columnListEndPos = $columnEndPos.after();
+            // Climbs out of the containers the block is the last child of,
+            // to the first position with a following node.
+            let $boundary = $pos;
+            while (
+              $boundary.nodeAfter === null &&
+              $boundary.depth > 0 &&
+              isContainerNode($boundary.node().type)
+            ) {
+              $boundary = tr.doc.resolve($boundary.after());
+            }
+
+            const nextNode = $boundary.nodeAfter;
+            if (!nextNode) {
+              return false;
+            }
+
+            // The block to pull in: the next node itself or — when it's a
+            // container — its first leaf block.
+            const target = isContainerNode(nextNode.type)
+              ? getFirstLeafBlock(nextNode, $boundary.pos)
+              : { node: nextNode, beforePos: $boundary.pos };
+            if (!target) {
+              return false;
+            }
 
             if (dispatch) {
-              // Position before first block in next column, or first block
-              // after columnList if there is no next column.
-              const nextBlockBeforePos =
-                $columnEndPos.pos === columnListEndPos - 1
-                  ? columnListEndPos
-                  : $columnEndPos.pos + 1;
-              const nextBlockInfo = getBlockInfoFromResolvedPos(
-                tr.doc.resolve(nextBlockBeforePos),
+              const containersToFix = getAncestorContainers(
+                tr.doc,
+                target.beforePos,
               );
 
               tr.delete(
-                nextBlockInfo.bnBlock.beforePos,
-                nextBlockInfo.bnBlock.afterPos,
-              );
-              fixColumnList(
-                tr,
-                columnListEndPos - $columnEndPos.node().nodeSize,
+                target.beforePos,
+                target.beforePos + target.node.nodeSize,
               );
-              tr.insert($blockEndPos.pos, nextBlockInfo.bnBlock.node);
+              tr.insert(blockInfo.bnBlock.afterPos, target.node);
+              fixContainersById(tr, containersToFix);
               tr.setSelection(
-                TextSelection.near(tr.doc.resolve(nextBlockBeforePos)),
+                TextSelection.near(tr.doc.resolve(target.beforePos)),
               );
             }
 
@@ -577,7 +699,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
         () =>
           commands.command(({ state }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
             const { blockContent } = blockInfo;
@@ -611,7 +733,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
                 state.doc,
                 blockInfo.bnBlock.beforePos,
               );
-              if (!nextBlockInfo || !nextBlockInfo.isBlockContainer) {
+              if (!nextBlockInfo || !nextBlockInfo.isWrappedBlock) {
                 return false;
               }
 
@@ -653,7 +775,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
         () =>
           commands.command(({ state }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -666,7 +788,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
                 state.doc,
                 blockInfo.bnBlock.beforePos,
               );
-              if (!nextBlockInfo || !nextBlockInfo.isBlockContainer) {
+              if (!nextBlockInfo || !nextBlockInfo.isWrappedBlock) {
                 return false;
               }
 
@@ -715,7 +837,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
           commands.command(({ state }) => {
             const blockInfo = getBlockInfoFromSelection(state);
 
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -730,7 +852,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
             if (!nextBlockInfo) {
               return false;
             }
-            if (!nextBlockInfo.isBlockContainer) {
+            if (!nextBlockInfo.isWrappedBlock) {
               return false;
             }
 
@@ -770,7 +892,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
         () =>
           commands.command(({ state, tr }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
             const { bnBlock: blockContainer, blockContent } = blockInfo;
@@ -859,12 +981,128 @@ export const KeyboardShortcutsExtension = Extension.create<{
 
             return false;
           }),
+        // Enter inside the content of a container that has children of its own
+        // (a toggle's title): everything after the cursor becomes a new first
+        // child, and the cursor moves into it. At the end of the title that's
+        // a new empty first child. Without this, the generic split below would
+        // try to split the container itself.
+        () =>
+          commands.command(({ state, tr, dispatch }) => {
+            const blockInfo = getBlockInfoFromSelection(state);
+            if (
+              !blockInfo.isWrappedBlock ||
+              !blockInfo.childContainer ||
+              !isContentContainerNode(blockInfo.bnBlock.node)
+            ) {
+              return false;
+            }
+            const { blockContent, childContainer } = blockInfo;
+
+            const titleEndPos = blockContent.afterPos - 1;
+            if (
+              state.selection.from < blockContent.beforePos + 1 ||
+              state.selection.to > titleEndPos
+            ) {
+              return false;
+            }
+
+            if (dispatch) {
+              // The tail of the title — empty when the cursor is at its end.
+              const tail = blockContent.node.content.cut(
+                state.selection.to - blockContent.beforePos - 1,
+              );
+              const newChild = state.schema.nodes[
+                "blockContainer"
+              ].createAndFill(
+                undefined,
+                state.schema.nodes["paragraph"].create(undefined, tail),
+              )!;
+
+              // Removes the tail (and anything selected) from the title, then
+              // prepends it to the container's children.
+              tr.delete(state.selection.from, titleEndPos);
+              const insertionPos = tr.mapping.map(childContainer.beforePos + 1);
+              tr.insert(insertionPos, newChild);
+              tr.setSelection(
+                TextSelection.near(tr.doc.resolve(insertionPos + 1)),
+              );
+              tr.scrollIntoView();
+            }
+
+            return true;
+          }),
+        // If the block is empty and the last child of a container with
+        // `exitOnEnter` behavior (the default for containers), moves the
+        // block out to after the container — one level per press, list-style.
+        // Without this, Enter only ever creates new blocks *within* the
+        // container, so a trailing container could trap the cursor.
+        () =>
+          commands.command(({ state, tr, dispatch }) => {
+            const blockInfo = getBlockInfoFromSelection(state);
+            if (!blockInfo.isWrappedBlock) {
+              return false;
+            }
+
+            const selectionEmpty =
+              state.selection.anchor === state.selection.head;
+            const blockEmpty = blockInfo.blockContent.node.childCount === 0;
+            if (!selectionEmpty || !blockEmpty) {
+              return false;
+            }
+
+            const $pos = tr.doc.resolve(blockInfo.bnBlock.beforePos);
+            const parentBlock = $pos.node();
+            if (!isContainerNode(parentBlock.type)) {
+              return false;
+            }
+
+            // Only fires on the container's last child.
+            if (tr.doc.resolve(blockInfo.bnBlock.afterPos).nodeAfter !== null) {
+              return false;
+            }
+
+            const parentChildren = getChildrenConfig(
+              this.options.editor.schema.blockSpecs[parentBlock.type.name]
+                ?.config ?? {},
+            );
+            if (
+              parentChildren &&
+              !resolveChildren(parentChildren).exitOnEnter
+            ) {
+              return false;
+            }
+
+            const containerAfterPos = $pos.after();
+
+            if (dispatch) {
+              const containersToFix = getAncestorContainers(
+                tr.doc,
+                blockInfo.bnBlock.beforePos,
+              );
+
+              tr.delete(
+                blockInfo.bnBlock.beforePos,
+                blockInfo.bnBlock.afterPos,
+              );
+              // The container's after-position, mapped through the deletion
+              // (and any schema-driven refill it triggered).
+              const insertionPos = tr.mapping.map(containerAfterPos);
+              tr.insert(insertionPos, blockInfo.bnBlock.node);
+              fixContainersById(tr, containersToFix);
+              tr.setSelection(
+                TextSelection.near(tr.doc.resolve(insertionPos + 1)),
+              );
+              tr.scrollIntoView();
+            }
+
+            return true;
+          }),
         // Creates a new block and moves the selection to it if the current one is empty, while the selection is also
         // empty & at the start of the block.
         () =>
           commands.command(({ state, dispatch, tr }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
             const { bnBlock: blockContainer, blockContent } = blockInfo;
@@ -920,7 +1158,7 @@ export const KeyboardShortcutsExtension = Extension.create<{
         () =>
           commands.command(({ state, chain }) => {
             const blockInfo = getBlockInfoFromSelection(state);
-            if (!blockInfo.isBlockContainer) {
+            if (!blockInfo.isWrappedBlock) {
               return false;
             }
             const { blockContent } = blockInfo;
diff --git a/packages/core/src/extensions/tiptap-extensions/UniqueID/UniqueID.ts b/packages/core/src/extensions/tiptap-extensions/UniqueID/UniqueID.ts
index 7ab30b78aa..c6c57a72c9 100644
--- a/packages/core/src/extensions/tiptap-extensions/UniqueID/UniqueID.ts
+++ b/packages/core/src/extensions/tiptap-extensions/UniqueID/UniqueID.ts
@@ -67,9 +67,12 @@ const UniqueID = Extension.create({
       setIdAttribute: false,
       isWithinEditor: undefined as ((element: Element) => boolean) | undefined,
       generateID: () => {
-        // Use mock ID if tests are running.
-        if (typeof window !== "undefined" && (window as any).__TEST_OPTIONS) {
-          const testOptions = (window as any).__TEST_OPTIONS;
+        // Use mock ID if tests are running. Resolved off `globalThis` rather
+        // than a bare `window` so that tests running in the plain `node`
+        // environment (no `window`) still get deterministic IDs.
+        const testHost: any = (globalThis as any).window ?? globalThis;
+        if (testHost.__TEST_OPTIONS) {
+          const testOptions = testHost.__TEST_OPTIONS;
           if (testOptions.mockID === undefined) {
             testOptions.mockID = 0;
           } else {
diff --git a/packages/core/src/fonts/inter.css b/packages/core/src/fonts/inter.css
index 57337cdd50..6e152551bf 100644
--- a/packages/core/src/fonts/inter.css
+++ b/packages/core/src/fonts/inter.css
@@ -9,7 +9,7 @@
     local(""),
     url("./inter-v12-latin/inter-v12-latin-100.woff2") format("woff2"),
     /* Chrome 26+, Opera 23+, Firefox 39+ */
-      url("./inter-v12-latin/inter-v12-latin-100.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
+    url("./inter-v12-latin/inter-v12-latin-100.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
 }
 /* inter-200 - latin */
 @font-face {
@@ -20,7 +20,7 @@
     local(""),
     url("./inter-v12-latin/inter-v12-latin-200.woff2") format("woff2"),
     /* Chrome 26+, Opera 23+, Firefox 39+ */
-      url("./inter-v12-latin/inter-v12-latin-200.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
+    url("./inter-v12-latin/inter-v12-latin-200.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
 }
 /* inter-300 - latin */
 @font-face {
@@ -31,7 +31,7 @@
     local(""),
     url("./inter-v12-latin/inter-v12-latin-300.woff2") format("woff2"),
     /* Chrome 26+, Opera 23+, Firefox 39+ */
-      url("./inter-v12-latin/inter-v12-latin-300.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
+    url("./inter-v12-latin/inter-v12-latin-300.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
 }
 /* inter-regular - latin */
 @font-face {
@@ -42,7 +42,7 @@
     local(""),
     url("./inter-v12-latin/inter-v12-latin-regular.woff2") format("woff2"),
     /* Chrome 26+, Opera 23+, Firefox 39+ */
-      url("./inter-v12-latin/inter-v12-latin-regular.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
+    url("./inter-v12-latin/inter-v12-latin-regular.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
 }
 /* inter-500 - latin */
 @font-face {
@@ -53,7 +53,7 @@
     local(""),
     url("./inter-v12-latin/inter-v12-latin-500.woff2") format("woff2"),
     /* Chrome 26+, Opera 23+, Firefox 39+ */
-      url("./inter-v12-latin/inter-v12-latin-500.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
+    url("./inter-v12-latin/inter-v12-latin-500.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
 }
 /* inter-600 - latin */
 @font-face {
@@ -64,7 +64,7 @@
     local(""),
     url("./inter-v12-latin/inter-v12-latin-600.woff2") format("woff2"),
     /* Chrome 26+, Opera 23+, Firefox 39+ */
-      url("./inter-v12-latin/inter-v12-latin-600.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
+    url("./inter-v12-latin/inter-v12-latin-600.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
 }
 /* inter-700 - latin */
 @font-face {
@@ -75,7 +75,7 @@
     local(""),
     url("./inter-v12-latin/inter-v12-latin-700.woff2") format("woff2"),
     /* Chrome 26+, Opera 23+, Firefox 39+ */
-      url("./inter-v12-latin/inter-v12-latin-700.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
+    url("./inter-v12-latin/inter-v12-latin-700.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
 }
 /* inter-800 - latin */
 @font-face {
@@ -86,7 +86,7 @@
     local(""),
     url("./inter-v12-latin/inter-v12-latin-800.woff2") format("woff2"),
     /* Chrome 26+, Opera 23+, Firefox 39+ */
-      url("./inter-v12-latin/inter-v12-latin-800.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
+    url("./inter-v12-latin/inter-v12-latin-800.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
 }
 /* inter-900 - latin */
 @font-face {
@@ -97,5 +97,5 @@
     local(""),
     url("./inter-v12-latin/inter-v12-latin-900.woff2") format("woff2"),
     /* Chrome 26+, Opera 23+, Firefox 39+ */
-      url("./inter-v12-latin/inter-v12-latin-900.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
+    url("./inter-v12-latin/inter-v12-latin-900.woff") format("woff"); /* Chrome 6+, Firefox 3.6+, IE 9+, Safari 5.1+ */
 }
diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index b4f220e1e2..fe5a7053d3 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -1,6 +1,10 @@
 export * from "./api/blockManipulation/commands/insertBlocks/insertBlocks.js";
 export * from "./api/blockManipulation/commands/replaceBlocks/replaceBlocks.js";
-export * from "./api/blockManipulation/commands/replaceBlocks/util/fixColumnList.js";
+// The rest of the container machinery — repair, navigation, UI info, the node
+// groups and the generated node names — is on `@blocknote/core/internal`.
+// `isContainerNode` stays here: it answers a question about the *document*,
+// which integrations legitimately ask.
+export { isContainerNode } from "./api/blockManipulation/containers/fixContainer.js";
 export * from "./api/blockManipulation/commands/updateBlock/updateBlock.js";
 export * from "./api/exporters/html/externalHTMLExporter.js";
 export * from "./api/exporters/html/internalHTMLSerializer.js";
diff --git a/packages/core/src/internal.ts b/packages/core/src/internal.ts
new file mode 100644
index 0000000000..5f16bd1fe3
--- /dev/null
+++ b/packages/core/src/internal.ts
@@ -0,0 +1,75 @@
+/**
+ * `@blocknote/core/internal`
+ *
+ * BlockNote's own machinery, exposed so the packages built on top of core
+ * (`@blocknote/react`, `@blocknote/xl-multi-column`, …) and BlockNote's tests
+ * can reach it — not part of the public API. Anything here may change in any
+ * release, without a major version bump or a deprecation.
+ *
+ * The public counterparts stay on the root entrypoint: `isContainerType`,
+ * `isContainerNode`, and the `children` config types (`ChildrenConfig`,
+ * `ChildrenAllow`, `ChildSlot`, `ChildCount`).
+ */
+
+// How a `children` config compiles to a ProseMirror content expression, and the
+// node groups and generated node names that fall out of it.
+export {
+  BLOCK_GROUP_CHILD_GROUP,
+  CHILD_CONTAINER_GROUP,
+  CONTAINER_CONTENT_GROUP,
+  CONTAINER_NODE_PRIORITY,
+  blockTypeOfContainerChildrenNode,
+  blockTypeOfContainerContentNode,
+  childrenContentExpression,
+  containerChildrenNodeName,
+  containerContentNodeName,
+  containerNodePriority,
+  getChildrenConfig,
+  getContentContainerNodeTypes,
+  getMinChildCount,
+  isContentContainerNode,
+  isPlaceableAnywhere,
+  resolveChildren,
+  type ContainerTypeContext,
+} from "./schema/blocks/children.js";
+
+// Validation of `children` configs, run when a schema is built.
+export {
+  slotAccepts,
+  validateChildrenConfigs,
+  validateContainerRunsBefore,
+} from "./schema/blocks/validateChildren.js";
+
+export { assertContainerSchemaInvariants } from "./schema/blocks/assertSchemaInvariants.js";
+
+// The attributes a container block's root element carries, and the three ways
+// they get there (node view, HTML serialization, framework render).
+export {
+  applyContainerAttributes,
+  fillContainerAttributes,
+  getContainerAttributes,
+} from "./schema/blocks/containerAttributes.js";
+
+// Repairing a container after its children changed.
+export {
+  fixContainer,
+  fixContainersById,
+  flattenNonInsertableBlocks,
+  isEmptyContainerChild,
+  removeEmptyChildren,
+} from "./api/blockManipulation/containers/fixContainer.js";
+
+// Position-based navigation through arbitrarily nested containers.
+export {
+  ascendToInsertablePos,
+  descendToFirstInsertionPos,
+  descendToLastInsertionPos,
+  getAncestorContainers,
+  getFirstLeafBlock,
+} from "./api/blockManipulation/containers/containerNav.js";
+
+// What the side menu and drag handle need to know about a schema's containers.
+export {
+  getContainerUIInfo,
+  type ContainerUIInfo,
+} from "./api/blockManipulation/containers/containerUI.js";
diff --git a/packages/core/src/schema/blocks/assertSchemaInvariants.ts b/packages/core/src/schema/blocks/assertSchemaInvariants.ts
new file mode 100644
index 0000000000..d5053b3617
--- /dev/null
+++ b/packages/core/src/schema/blocks/assertSchemaInvariants.ts
@@ -0,0 +1,62 @@
+import { Fragment, type Schema } from "prosemirror-model";
+
+import { isContainerNode } from "../../api/blockManipulation/containers/fixContainer.js";
+
+/**
+ * Checks the two structural properties the rest of the container machinery
+ * assumes, once, when the ProseMirror schema is built.
+ *
+ * Both used to be guaranteed only by a chain of implicit reasoning spread
+ * across several files. Asserting them here turns a class of "works until it
+ * silently doesn't" bugs into a startup error naming the cause.
+ */
+export function assertContainerSchemaInvariants(pmSchema: Schema) {
+  assertBlockGroupFillsWithBlockContainer(pmSchema);
+  assertContainersAreFillable(pmSchema);
+}
+
+/**
+ * `blockGroup` must auto-fill with `blockContainer` rather than with some
+ * container block type.
+ *
+ * Today this holds because container nodes register below `blockContainer`'s
+ * priority, which drives TipTap's registration order, which drives the order
+ * ProseMirror resolves a group into types, which drives what `fillBefore`
+ * picks. That's four implicit links, and Yjs document initialization depends
+ * on the result (see `FixUpSchema`, which reads the first auto-filled child
+ * expecting it to be the id-carrying `blockContainer`).
+ */
+function assertBlockGroupFillsWithBlockContainer(pmSchema: Schema) {
+  const defaultType = pmSchema.nodes["blockGroup"]?.contentMatch.defaultType;
+
+  if (defaultType?.name !== "blockContainer") {
+    throw new Error(
+      `BlockNote schema invariant broken: \`blockGroup\` auto-fills with "${defaultType?.name}" instead of "blockContainer". ` +
+        "Container block nodes must register at a lower priority than `blockContainer` (see CONTAINER_NODE_PRIORITY). " +
+        "Yjs document initialization depends on this (see FixUpSchema).",
+    );
+  }
+}
+
+/**
+ * Every container must be creatable empty, or inserting one throws a raw
+ * ProseMirror error at the call site instead of here.
+ *
+ * This is the empirical version of "is this `children` config buildable" — it
+ * asks ProseMirror rather than trying to re-derive the answer from the config,
+ * so it catches combinations no hand-written check would think to cover.
+ */
+function assertContainersAreFillable(pmSchema: Schema) {
+  for (const type of Object.values(pmSchema.nodes)) {
+    if (!isContainerNode(type)) {
+      continue;
+    }
+
+    if (!type.contentMatch.fillBefore(Fragment.empty, true)) {
+      throw new Error(
+        `Container block "${type.name}" can never be created empty: its \`children\` config compiles to \`${type.spec.content}\`, ` +
+          "which ProseMirror cannot auto-fill. Lower the minimum child count, or allow regular blocks in the first slot.",
+      );
+    }
+  }
+}
diff --git a/packages/core/src/schema/blocks/children.test.ts b/packages/core/src/schema/blocks/children.test.ts
new file mode 100644
index 0000000000..6436731f28
--- /dev/null
+++ b/packages/core/src/schema/blocks/children.test.ts
@@ -0,0 +1,134 @@
+// @vitest-environment node
+import { describe, expect, it } from "vite-plus/test";
+
+import { childrenContentExpression, resolveChildren } from "./children.js";
+import type { ChildrenConfig } from "./types.js";
+
+// Pretend schema: `column` and `gridCell` are containers, everything else is a
+// regular block.
+const CONTAINER_TYPES = ["column", "gridCell", "cardHeader", "cardBody"];
+const ctx = {
+  isContainerBlockType: (type: string) => CONTAINER_TYPES.includes(type),
+  containerBlockTypes: () => CONTAINER_TYPES,
+};
+
+// The content expression is the whole enforcement story — if this table is
+// right, `allow`/`min`/`max`/`sequence` are enforced by ProseMirror itself.
+const CASES: [string, ChildrenConfig, string][] = [
+  ["any block, at least one (the default)", {}, "blockGroupChild+"],
+  ["any block, possibly none", { min: 0 }, "blockGroupChild*"],
+  ["any block, exactly one", { min: 1, max: 1 }, "blockGroupChild"],
+  ["any block, two or more", { min: 2 }, "blockGroupChild{2,}"],
+  ["any block, two to four", { min: 2, max: 4 }, "blockGroupChild{2,4}"],
+  ["any block, at most one", { min: 0, max: 1 }, "blockGroupChild?"],
+  ["any block, exactly three", { min: 3, max: 3 }, "blockGroupChild{3}"],
+  ["regular blocks only", { allow: { containers: false } }, "blockContainer+"],
+  [
+    "one container type only",
+    { allow: { blocks: false, containers: ["column"] }, min: 2 },
+    "column{2,}",
+  ],
+  [
+    "regular blocks or one container type",
+    { allow: { containers: ["column"] } },
+    "(blockContainer | column)+",
+  ],
+  [
+    "any container but no regular blocks",
+    { allow: { blocks: false, containers: true } },
+    "(column | gridCell | cardHeader | cardBody)+",
+  ],
+  [
+    "ordered: header then body",
+    {
+      sequence: [
+        { allow: { blocks: false, containers: ["cardHeader"] } },
+        { allow: { blocks: false, containers: ["cardBody"] } },
+      ],
+    },
+    "cardHeader cardBody",
+  ],
+  [
+    "ordered: optional header, then one or more regular blocks",
+    {
+      sequence: [
+        {
+          allow: { blocks: false, containers: ["cardHeader"] },
+          count: { max: 1 },
+        },
+        { allow: { containers: false }, count: { min: 1 } },
+      ],
+    },
+    "cardHeader? blockContainer+",
+  ],
+  [
+    "ordered: body then a trailing citation",
+    {
+      sequence: [
+        { allow: { containers: false }, count: { min: 1 } },
+        { allow: { blocks: false, containers: ["cardBody"] } },
+      ],
+    },
+    "blockContainer+ cardBody",
+  ],
+];
+
+describe("childrenContentExpression", () => {
+  it.each(CASES)("%s", (_name, config, expected) => {
+    expect(childrenContentExpression(config, ctx)).toBe(expected);
+  });
+
+  // `fillBefore` picks the first matching type in a union, and filling with
+  // `blockContainer` (rather than another container) is what keeps auto-fill
+  // from recursing through nested containers.
+  it("orders blockContainer first in a union", () => {
+    expect(
+      childrenContentExpression({ allow: { containers: ["column"] } }, ctx),
+    ).toMatch(/^\(blockContainer \|/);
+  });
+});
+
+describe("resolveChildren", () => {
+  it("treats the uniform form as a one-slot sequence", () => {
+    const uniform = resolveChildren({ allow: { containers: false }, min: 2 });
+    const sequence = resolveChildren({
+      sequence: [{ allow: { containers: false }, count: { min: 2 } }],
+    });
+    expect(uniform.slots).toEqual(sequence.slots);
+  });
+
+  it("defaults a slot to exactly one child", () => {
+    expect(resolveChildren({ sequence: [{}] }).slots[0]).toMatchObject({
+      min: 1,
+      max: 1,
+    });
+  });
+
+  it("sums slot bounds into overall counts", () => {
+    const resolved = resolveChildren({
+      sequence: [{}, { count: { min: 1, max: 3 } }],
+    });
+    expect(resolved.minCount).toBe(2);
+    expect(resolved.maxCount).toBe(4);
+  });
+
+  it("reports an unbounded maximum when any slot is unbounded", () => {
+    expect(
+      resolveChildren({ sequence: [{}, { count: { min: 1 } }] }).maxCount,
+    ).toBeUndefined();
+  });
+
+  it("collapses `containers: false` to an empty list", () => {
+    expect(
+      resolveChildren({ allow: { containers: false } }).slots[0].containers,
+    ).toEqual([]);
+  });
+
+  it("returns the same object for the same config", () => {
+    // Downstream code resolves the same config object on every node build and
+    // repair pass, and must never mutate the user's object.
+    const config: ChildrenConfig = { min: 1 };
+    expect(resolveChildren(config)).toBe(resolveChildren(config));
+    expect(config).toEqual({ min: 1 });
+  });
+});
diff --git a/packages/core/src/schema/blocks/children.ts b/packages/core/src/schema/blocks/children.ts
new file mode 100644
index 0000000000..18761ea485
--- /dev/null
+++ b/packages/core/src/schema/blocks/children.ts
@@ -0,0 +1,239 @@
+import type { Node, NodeType, Schema } from "prosemirror-model";
+
+import type {
+  BlockConfig,
+  ChildrenConfig,
+  ChildCount,
+  ChildSlot,
+  ResolvedChildren,
+  ResolvedSlot,
+} from "./types.js";
+
+export const CHILD_CONTAINER_GROUP = "childContainer";
+
+export const BLOCK_GROUP_CHILD_GROUP = "blockGroupChild";
+
+// Not `blockContent` — that's a legal child of `blockContainer`, so a paste
+// could produce an unrepresentable `blockContainer > toggle__content`.
+export const CONTAINER_CONTENT_GROUP = "containerContent";
+
+// `__` because PM's expression parser only accepts word characters in node names.
+const CONTENT_NODE_SUFFIX = "__content";
+const CHILDREN_NODE_SUFFIX = "__children";
+
+export function containerContentNodeName(blockType: string): string {
+  return `${blockType}${CONTENT_NODE_SUFFIX}`;
+}
+
+export function containerChildrenNodeName(blockType: string): string {
+  return `${blockType}${CHILDREN_NODE_SUFFIX}`;
+}
+
+export function blockTypeOfContainerContentNode(
+  nodeName: string,
+): string | undefined {
+  return nodeName.endsWith(CONTENT_NODE_SUFFIX)
+    ? nodeName.slice(0, -CONTENT_NODE_SUFFIX.length)
+    : undefined;
+}
+
+export function blockTypeOfContainerChildrenNode(
+  nodeName: string,
+): string | undefined {
+  return nodeName.endsWith(CHILDREN_NODE_SUFFIX)
+    ? nodeName.slice(0, -CHILDREN_NODE_SUFFIX.length)
+    : undefined;
+}
+
+// Whether `node` is a container that has its own content (children live in
+// a generated `__children` node). Not the same as `isContainerNode`.
+export function isContentContainerNode(node: Node): boolean {
+  return !!node.firstChild?.type.isInGroup(CONTAINER_CONTENT_GROUP);
+}
+
+export function getContentContainerNodeTypes(
+  schema: Schema,
+  blockType: string,
+): { contentType: NodeType; childrenType: NodeType } | undefined {
+  const contentType = schema.nodes[containerContentNodeName(blockType)];
+  const childrenType = schema.nodes[containerChildrenNodeName(blockType)];
+
+  return contentType && childrenType
+    ? { contentType, childrenType }
+    : undefined;
+}
+
+// Below `blockContainer`'s priority (50) so PM's `fillBefore` picks
+// `blockContainer` first, avoiding recursion through nested containers.
+export const CONTAINER_NODE_PRIORITY = 40;
+
+const CONTAINER_PRIORITY_BAND = { min: 30, max: 49 };
+const DEFAULT_SPEC_PRIORITY = 101;
+
+// Maps `sortByDependencies` priority into the container band (30–49).
+// Preserves relative order but keeps all containers below regular blocks.
+export function containerNodePriority(priority: number | undefined): number {
+  if (priority === undefined) {
+    return CONTAINER_NODE_PRIORITY;
+  }
+
+  const steps = Math.round((priority - DEFAULT_SPEC_PRIORITY) / 10);
+
+  return Math.min(
+    CONTAINER_PRIORITY_BAND.max,
+    Math.max(CONTAINER_PRIORITY_BAND.min, CONTAINER_NODE_PRIORITY + steps),
+  );
+}
+
+export function getChildrenConfig(config: {
+  children?: ChildrenConfig;
+}): ChildrenConfig | undefined {
+  return config.children;
+}
+
+export function isContainerType(config: {
+  children?: ChildrenConfig;
+}): boolean {
+  return config.children !== undefined;
+}
+
+export function isPlaceableAnywhere(config: {
+  placement?: BlockConfig["placement"];
+}): boolean {
+  return config.placement !== "containerOnly";
+}
+
+const resolvedCache = new WeakMap<ChildrenConfig, ResolvedChildren>();
+
+export function resolveChildren(children: ChildrenConfig): ResolvedChildren {
+  const cached = resolvedCache.get(children);
+  if (cached) {
+    return cached;
+  }
+
+  const slots: ResolvedSlot[] = children.sequence
+    ? children.sequence.map(resolveSlot)
+    : [
+        {
+          ...resolveAllow(children.allow),
+          min: children.min ?? 1,
+          max: children.max,
+        },
+      ];
+
+  let maxCount: number | undefined = 0;
+  for (const slot of slots) {
+    if (slot.max === undefined) {
+      maxCount = undefined;
+      break;
+    }
+    maxCount += slot.max;
+  }
+
+  const resolved: ResolvedChildren = {
+    slots,
+    minCount: slots.reduce((total, slot) => total + slot.min, 0),
+    maxCount,
+    default: children.default,
+    unwrapWhenEmptied: children.unwrapWhenEmptied ?? false,
+    exitOnEnter: children.exitOnEnter ?? true,
+  };
+
+  resolvedCache.set(children, resolved);
+  return resolved;
+}
+
+function resolveSlot(slot: ChildSlot): ResolvedSlot {
+  return { ...resolveAllow(slot.allow), ...resolveCount(slot.count) };
+}
+
+function resolveCount(count: ChildCount | undefined): {
+  min: number;
+  max: number | undefined;
+} {
+  if (count === undefined) {
+    return { min: 1, max: 1 };
+  }
+  if (typeof count === "number") {
+    return { min: count, max: count };
+  }
+  return { min: count.min ?? 0, max: count.max };
+}
+
+function resolveAllow(
+  allow: ChildrenConfig["allow"],
+): Pick<ResolvedSlot, "blocks" | "containers"> {
+  const containers = allow?.containers ?? true;
+  return {
+    blocks: allow?.blocks ?? true,
+    containers: containers === false ? [] : containers,
+  };
+}
+
+export function getMinChildCount(children: ChildrenConfig): number {
+  return resolveChildren(children).minCount;
+}
+
+export type ContainerTypeContext = {
+  isContainerBlockType: (blockType: string) => boolean;
+  containerBlockTypes: () => readonly string[];
+};
+
+export function childrenContentExpression(
+  children: ChildrenConfig,
+  ctx: ContainerTypeContext,
+): string {
+  return resolveChildren(children)
+    .slots.map((slot) => slotTerm(slot, ctx) + quantifier(slot.min, slot.max))
+    .join(" ");
+}
+
+function slotTerm(slot: ResolvedSlot, ctx: ContainerTypeContext): string {
+  // "Anything" is already a group, so use it rather than spelling out a union
+  // that would need rebuilding whenever the schema gains a container type.
+  if (slot.blocks && slot.containers === true) {
+    return BLOCK_GROUP_CHILD_GROUP;
+  }
+
+  const terms: string[] = [];
+  // `blockContainer` FIRST: PM's `fillBefore` picks the first matching type in
+  // a union, and filling with `blockContainer` (rather than another container)
+  // keeps auto-fill from recursing through nested containers.
+  if (slot.blocks) {
+    terms.push("blockContainer");
+  }
+  // Deliberately expanded rather than emitting the `childContainer` group —
+  // that group also contains `blockGroup`, which is not a block.
+  terms.push(
+    ...(slot.containers === true ? ctx.containerBlockTypes() : slot.containers),
+  );
+
+  if (terms.length === 0) {
+    // Validation rejects this first; this is a bug-guard, not a user-facing
+    // error path.
+    throw new Error(
+      "Container slot allows nothing. This is a bug in BlockNote.",
+    );
+  }
+
+  return terms.length === 1 ? terms[0] : `(${terms.join(" | ")})`;
+}
+
+function quantifier(min: number, max: number | undefined): string {
+  if (max === undefined) {
+    if (min === 0) {
+      return "*";
+    }
+    if (min === 1) {
+      return "+";
+    }
+    return `{${min},}`;
+  }
+  if (min === max) {
+    return max === 1 ? "" : `{${min}}`;
+  }
+  if (min === 0 && max === 1) {
+    return "?";
+  }
+  return `{${min},${max}}`;
+}
diff --git a/packages/core/src/schema/blocks/containerAttributes.ts b/packages/core/src/schema/blocks/containerAttributes.ts
new file mode 100644
index 0000000000..e0657b6e88
--- /dev/null
+++ b/packages/core/src/schema/blocks/containerAttributes.ts
@@ -0,0 +1,75 @@
+import { camelToDataKebab } from "../../util/string.js";
+import { PropSchema, Props } from "../propTypes.js";
+
+export function getContainerAttributes<PSchema extends PropSchema>(
+  blockType: string,
+  blockProps: Partial<Props<PSchema>>,
+  propSchema: PSchema,
+  id: string | undefined,
+): Record<string, string> {
+  const attributes: Record<string, string> = { "data-node-type": blockType };
+
+  for (const [prop, value] of Object.entries(blockProps)) {
+    if (value === undefined || value === propSchema[prop]?.default) {
+      continue;
+    }
+    attributes[camelToDataKebab(prop)] = `${value}`;
+  }
+
+  if (id) {
+    attributes["data-id"] = id;
+  }
+
+  return attributes;
+}
+
+export function applyContainerAttributes<PSchema extends PropSchema>(
+  dom: HTMLElement | DocumentFragment | undefined | null,
+  blockType: string,
+  blockProps: Partial<Props<PSchema>>,
+  propSchema: PSchema,
+  id: string | undefined,
+) {
+  const element = dom as HTMLElement | undefined;
+  if (!element || typeof element.setAttribute !== "function") {
+    return;
+  }
+
+  const attributes = getContainerAttributes(
+    blockType,
+    blockProps,
+    propSchema,
+    id,
+  );
+
+  for (const prop of Object.keys(blockProps)) {
+    const attr = camelToDataKebab(prop);
+    if (!(attr in attributes)) {
+      element.removeAttribute(attr);
+    }
+  }
+  for (const [attr, value] of Object.entries(attributes)) {
+    element.setAttribute(attr, value);
+  }
+}
+
+// Like `applyContainerAttributes` but won't overwrite existing attributes.
+export function fillContainerAttributes<PSchema extends PropSchema>(
+  dom: HTMLElement,
+  blockType: string,
+  blockProps: Partial<Props<PSchema>>,
+  propSchema: PSchema,
+) {
+  const attributes = getContainerAttributes(
+    blockType,
+    blockProps,
+    propSchema,
+    undefined,
+  );
+
+  for (const [attr, value] of Object.entries(attributes)) {
+    if (!dom.hasAttribute(attr)) {
+      dom.setAttribute(attr, value);
+    }
+  }
+}
diff --git a/packages/core/src/schema/blocks/containerParse.browser.test.ts b/packages/core/src/schema/blocks/containerParse.browser.test.ts
new file mode 100644
index 0000000000..6a727a7e8b
--- /dev/null
+++ b/packages/core/src/schema/blocks/containerParse.browser.test.ts
@@ -0,0 +1,339 @@
+import { Fragment } from "prosemirror-model";
+import { AllSelection } from "prosemirror-state";
+import {
+  afterAll,
+  beforeAll,
+  beforeEach,
+  describe,
+  expect,
+  it,
+} from "vite-plus/test";
+
+import { BlockNoteSchema } from "../../blocks/BlockNoteSchema.js";
+import { defaultBlockSpecs } from "../../blocks/defaultBlocks.js";
+import { BlockNoteEditor } from "../../editor/BlockNoteEditor.js";
+import { createBlockSpec } from "./createSpec.js";
+
+// Every test here goes through `tryParseHTMLToBlocks`, which parses real HTML
+// into a real DOM (`document.implementation.createHTMLDocument` in
+// `api/parsers/html/util/nestedLists.ts`) before ProseMirror's parser ever runs
+// — and the clipboard test additionally needs a mounted view for
+// `view.serializeForClipboard`. Parsing HTML *is* the capability under test, so
+// this whole suite runs against a real browser engine rather than jsdom's.
+
+const renderDiv = () => {
+  const dom = document.createElement("div");
+  return { dom, contentDOM: dom };
+};
+
+// A pure container that recognizes its own external HTML. Before containers
+// went through `getParseRules`, `parse` was silently dropped for them and this
+// produced nothing at all.
+const Card = createBlockSpec(
+  {
+    type: "card" as const,
+    propSchema: { tone: { default: "neutral" } },
+    content: "none",
+    children: {},
+  },
+  {
+    render: renderDiv,
+    parse: (el) =>
+      el.classList.contains("card")
+        ? { tone: el.getAttribute("data-tone") ?? undefined }
+        : undefined,
+  },
+)();
+
+// The same, but taking over the parsing of its own body.
+const Quote = createBlockSpec(
+  {
+    type: "quote" as const,
+    propSchema: {},
+    content: "none",
+    children: {},
+  },
+  {
+    render: renderDiv,
+    parse: (el) => (el.tagName === "BLOCKQUOTE" ? {} : undefined),
+    // Returns inline nodes — the natural thing to build from an element — and
+    // relies on `toContainerChildren` to place them.
+    parseContent: ({ el, schema }) =>
+      Fragment.from(schema.text(el.textContent?.trim() || "empty")),
+  },
+)();
+
+// A container with its own content, to exercise the two generated nodes
+// through the clipboard.
+const Toggle = createBlockSpec(
+  {
+    type: "toggle" as const,
+    propSchema: { open: { default: true } },
+    content: "inline",
+    children: {},
+  },
+  { render: renderDiv },
+)();
+
+// A content-bearing container whose `parseContent` returns a leading run of
+// inline nodes followed by a block — the shape that has to split across the
+// two generated nodes.
+const Section = createBlockSpec(
+  {
+    type: "section" as const,
+    propSchema: {},
+    content: "inline",
+    children: {},
+  },
+  {
+    render: renderDiv,
+    parse: (el) => (el.tagName === "SECTION" ? {} : undefined),
+    parseContent: ({ el, schema }) =>
+      Fragment.fromArray([
+        schema.text(el.getAttribute("data-title") || "untitled"),
+        schema.nodes["paragraph"].create(
+          null,
+          schema.text(el.textContent?.trim() || "empty"),
+        ),
+      ]),
+  },
+)();
+
+const schema = BlockNoteSchema.create().extend({
+  blockSpecs: {
+    ...defaultBlockSpecs,
+    card: Card,
+    quote: Quote,
+    toggle: Toggle,
+    section: Section,
+  } as const,
+});
+
+let editor: BlockNoteEditor<any, any, any>;
+const div = document.createElement("div");
+
+beforeAll(() => {
+  document.body.appendChild(div);
+  editor = BlockNoteEditor.create({ schema }) as any;
+  editor.mount(div);
+});
+
+afterAll(() => {
+  editor._tiptapEditor.destroy();
+  div.remove();
+  editor = undefined as any;
+});
+
+beforeEach(() => {
+  editor.replaceBlocks(editor.document, [
+    { id: "p-0", type: "paragraph", content: "Paragraph 0" },
+  ]);
+});
+
+describe("container `parse`", () => {
+  it("parses an external element into a container, children intact", () => {
+    const blocks = editor.tryParseHTMLToBlocks(
+      '<div class="card" data-tone="warning"><p>First</p><h1>Second</h1></div>',
+    );
+
+    expect(blocks).toHaveLength(1);
+    expect(blocks[0].type).toBe("card");
+    expect(blocks[0].props.tone).toBe("warning");
+    // No `getContent` is supplied, so ProseMirror parses the children with the
+    // normal block rules and `findWrapping` adds the `blockContainer`s.
+    expect(blocks[0].children.map((child: any) => child.type)).toEqual([
+      "paragraph",
+      "heading",
+    ]);
+    expect(blocks[0].children[0].content).toEqual([
+      { type: "text", text: "First", styles: {} },
+    ]);
+  });
+
+  it("places inline nodes returned by `parseContent` into a child block", () => {
+    const blocks = editor.tryParseHTMLToBlocks(
+      "<blockquote>Quoted text</blockquote>",
+    );
+
+    expect(blocks).toHaveLength(1);
+    expect(blocks[0].type).toBe("quote");
+    expect(blocks[0].children.map((child: any) => child.type)).toEqual([
+      "paragraph",
+    ]);
+    expect(blocks[0].children[0].content).toEqual([
+      { type: "text", text: "Quoted text", styles: {} },
+    ]);
+  });
+
+  it("splits `parseContent` across a content-bearing container's two regions", () => {
+    const blocks = editor.tryParseHTMLToBlocks(
+      '<section data-title="Title">Body</section>',
+    );
+
+    expect(blocks).toHaveLength(1);
+    expect(blocks[0].type).toBe("section");
+    // The leading inline run is the block's own content; the block that
+    // follows it is a child.
+    expect(blocks[0].content).toEqual([
+      { type: "text", text: "Title", styles: {} },
+    ]);
+    expect(blocks[0].children.map((child: any) => child.type)).toEqual([
+      "paragraph",
+    ]);
+    expect(blocks[0].children[0].content).toEqual([
+      { type: "text", text: "Body", styles: {} },
+    ]);
+  });
+});
+
+describe("container HTML round-trip", () => {
+  const toggleBlocks = [
+    {
+      id: "t-0",
+      type: "toggle" as const,
+      props: { open: false },
+      content: "Title",
+      children: [
+        { id: "t-p-0", type: "paragraph" as const, content: "Body" },
+        { id: "t-p-1", type: "heading" as const, content: "Sub" },
+      ],
+    },
+  ];
+
+  const expectRoundTripped = (parsed: any[]) => {
+    expect(parsed).toHaveLength(1);
+    expect(parsed[0].type).toBe("toggle");
+    expect(parsed[0].props.open).toBe(false);
+    expect(parsed[0].content).toEqual([
+      { type: "text", text: "Title", styles: {} },
+    ]);
+    expect(
+      parsed[0].children.map((child: any) => [
+        child.type,
+        child.content?.[0]?.text,
+      ]),
+    ).toEqual([
+      ["paragraph", "Body"],
+      ["heading", "Sub"],
+    ]);
+  };
+
+  it("round-trips a content-bearing container through full HTML", () => {
+    editor.replaceBlocks(editor.document, toggleBlocks);
+
+    const html = editor.blocksToFullHTML(editor.document);
+    expect(html).toContain('data-node-type="toggle"');
+
+    expectRoundTripped(editor.tryParseHTMLToBlocks(html));
+  });
+
+  it("round-trips a content-bearing container through the clipboard", () => {
+    editor.replaceBlocks(editor.document, toggleBlocks);
+
+    // What a copy actually puts on the clipboard: ProseMirror's own
+    // serialization, which renders the generated content & children nodes.
+    const view = editor._tiptapEditor.view;
+    view.dispatch(view.state.tr.setSelection(new AllSelection(view.state.doc)));
+    const clipboardHTML = view.serializeForClipboard(
+      view.state.selection.content(),
+    ).dom.innerHTML;
+
+    expect(clipboardHTML).toContain('data-content-type="toggle"');
+    expect(clipboardHTML).toContain('data-children-of="toggle"');
+
+    expectRoundTripped(editor.tryParseHTMLToBlocks(clipboardHTML));
+  });
+
+  it("round-trips a content-bearing container through external HTML", () => {
+    editor.replaceBlocks(editor.document, toggleBlocks);
+
+    const html = editor.blocksToHTMLLossy(editor.document);
+    expect(html).toContain('data-node-type="toggle"');
+
+    expectRoundTripped(editor.tryParseHTMLToBlocks(html));
+  });
+
+  // Two children, because the one-child case passes either way. External HTML
+  // has no marker element for the container's own content, so an empty title
+  // leaves the parser reading a block element first — with nothing to satisfy
+  // the content node, it can't open the children node and every child used to
+  // land *after* the container.
+  it("round-trips an empty-titled container's children through external HTML", () => {
+    editor.replaceBlocks(editor.document, [
+      { ...toggleBlocks[0], content: undefined },
+    ]);
+
+    const html = editor.blocksToHTMLLossy(editor.document);
+    const parsed = editor.tryParseHTMLToBlocks(html);
+
+    expect(parsed).toHaveLength(1);
+    expect(parsed[0].type).toBe("toggle");
+    expect(
+      (parsed[0] as any).children.map((child: any) => [
+        child.type,
+        child.content?.[0]?.text,
+      ]),
+    ).toEqual([
+      ["paragraph", "Body"],
+      ["heading", "Sub"],
+    ]);
+  });
+});
+
+describe("container `runsBefore`", () => {
+  const ambiguous = (type: string) =>
+    createBlockSpec(
+      { type, propSchema: {}, content: "none", children: {} } as any,
+      {
+        render: renderDiv,
+        parse: (el: HTMLElement) =>
+          el.classList.contains("shared") ? {} : undefined,
+      },
+    );
+
+  const makeEditor = (betaRunsBefore?: string[]) => {
+    const alpha = ambiguous("alpha")();
+    const beta = ambiguous("beta")();
+    if (betaRunsBefore) {
+      (beta.implementation as any).runsBefore = betaRunsBefore;
+    }
+
+    return BlockNoteEditor.create({
+      schema: BlockNoteSchema.create().extend({
+        blockSpecs: { ...defaultBlockSpecs, alpha, beta } as any,
+      }),
+    }) as BlockNoteEditor<any, any, any>;
+  };
+
+  it("leaves the declaration order alone by default", () => {
+    const other = makeEditor();
+    try {
+      expect(
+        other.tryParseHTMLToBlocks('<div class="shared"><p>x</p></div>')[0]
+          .type,
+      ).toBe("alpha");
+    } finally {
+      other._tiptapEditor.destroy();
+    }
+  });
+
+  it("orders a container's parse rules before another container's", () => {
+    const other = makeEditor(["alpha"]);
+    try {
+      expect(
+        other.tryParseHTMLToBlocks('<div class="shared"><p>x</p></div>')[0]
+          .type,
+      ).toBe("beta");
+    } finally {
+      other._tiptapEditor.destroy();
+    }
+  });
+
+  it("rejects a `runsBefore` naming a regular block", () => {
+    // Container nodes all register below `blockContainer`, so this ordering is
+    // not something the schema could ever produce.
+    expect(() => makeEditor(["paragraph"])).toThrow(
+      /can never be ordered before a regular block/,
+    );
+  });
+});
diff --git a/packages/core/src/schema/blocks/createSpec.ts b/packages/core/src/schema/blocks/createSpec.ts
index b1e54d640a..ad4b48607a 100644
--- a/packages/core/src/schema/blocks/createSpec.ts
+++ b/packages/core/src/schema/blocks/createSpec.ts
@@ -1,11 +1,13 @@
-import { Editor, Node } from "@tiptap/core";
+import { Editor, Node, NodeViewRendererProps } from "@tiptap/core";
 import {
   DOMParser,
   Fragment,
   Node as PMNode,
+  Schema as PMSchema,
   TagParseRule,
 } from "@tiptap/pm/model";
 import { NodeView } from "@tiptap/pm/view";
+import { nodeToBlock } from "../../api/nodeConversions/nodeToBlock.js";
 import { mergeParagraphs } from "../../blocks/defaultBlockHelpers.js";
 import {
   Extension,
@@ -13,8 +15,22 @@ import {
 } from "../../editor/BlockNoteExtension.js";
 import { nonFormattingMarks } from "../markGroups.js";
 import { ignoreNonContentMutations } from "../nodeViewMutations.js";
+import { suggestionMarks } from "../../pm-nodes/suggestionMarks.js";
 import { PropSchema } from "../propTypes.js";
 import {
+  CHILD_CONTAINER_GROUP,
+  CONTAINER_CONTENT_GROUP,
+  type ContainerTypeContext,
+  childrenContentExpression,
+  containerChildrenNodeName,
+  containerContentNodeName,
+  containerNodePriority,
+  getChildrenConfig,
+  isPlaceableAnywhere,
+} from "./children.js";
+import { applyContainerAttributes } from "./containerAttributes.js";
+import {
+  applyDOMAttributes,
   getBlockFromNodeView,
   propsToAttributes,
   wrapInBlockStructure,
@@ -28,6 +44,23 @@ import {
   LooseBlockSpec,
 } from "./types.js";
 
+export type BlockSchemaContext = ContainerTypeContext;
+
+const NO_SCHEMA_CONTEXT: BlockSchemaContext = {
+  isContainerBlockType: (blockType) => {
+    throw new Error(
+      `Cannot resolve whether "${blockType}" is a container block without full schema context. ` +
+        "Blocks that use `children.allow.containers` must be registered through `BlockNoteSchema.create`.",
+    );
+  },
+  containerBlockTypes: () => {
+    throw new Error(
+      "Cannot resolve the schema's container block types without full schema context. " +
+        "Blocks that use `children.allow.containers` must be registered through `BlockNoteSchema.create`.",
+    );
+  },
+};
+
 // Function that causes events within non-selectable blocks to be handled by the
 // browser instead of the editor.
 export function applyNonSelectableBlockFix(nodeView: NodeView, editor: Editor) {
@@ -45,9 +78,45 @@ export function applyNonSelectableBlockFix(nodeView: NodeView, editor: Editor) {
   };
 }
 
-// Function that uses the 'parse' function of a blockConfig to create a
-// TipTap node's `parseHTML` property. This is only used for parsing content
-// from the clipboard.
+// Wraps inline runs from `parseContent` into paragraphs so they fit a
+// container's block content expression. A leading inline run in a
+// content-bearing container stays inline (it's the block's own content).
+function toContainerChildren(
+  fragment: Fragment,
+  schema: PMSchema,
+  hasOwnContent: boolean,
+): Fragment {
+  const out: PMNode[] = [];
+  let inlineRun: PMNode[] = [];
+  let seenBlock = false;
+
+  const flush = () => {
+    if (inlineRun.length === 0) {
+      return;
+    }
+    out.push(
+      ...(hasOwnContent && !seenBlock
+        ? inlineRun
+        : [schema.nodes["paragraph"].create(null, inlineRun)]),
+    );
+    inlineRun = [];
+  };
+
+  fragment.forEach((child) => {
+    if (child.isInline) {
+      inlineRun.push(child);
+      return;
+    }
+    flush();
+    seenBlock = true;
+    out.push(child);
+  });
+  flush();
+
+  return Fragment.fromArray(out);
+}
+
+// Creates `parseHTML` rules for clipboard parsing.
 export function getParseRules<
   TName extends string,
   TProps extends PropSchema,
@@ -55,12 +124,17 @@ export function getParseRules<
 >(
   config: BlockConfig<TName, TProps, TContent>,
   implementation: BlockImplementation<TName, TProps, TContent>,
+  kind: "regular" | "container" = "regular",
 ) {
+  const isContainer = kind === "container";
+
   const rules: TagParseRule[] = [
-    {
-      tag: "[data-content-type=" + config.type + "]",
-      contentElement: ".bn-inline-content",
-    },
+    isContainer
+      ? { tag: `[data-node-type=${config.type}]` }
+      : {
+          tag: "[data-content-type=" + config.type + "]",
+          contentElement: ".bn-inline-content",
+        },
   ];
 
   if (implementation.parse) {
@@ -81,10 +155,25 @@ export function getParseRules<
       },
       // Because we do the parsing ourselves, we want to preserve whitespace for content we've parsed
       preserveWhitespace: true,
-      getContent:
-        config.content === "inline" ||
-        config.content === "none" ||
-        config.content === "plain"
+      getContent: isContainer
+        ? implementation.parseContent
+          ? (node, schema) =>
+              toContainerChildren(
+                implementation.parseContent!({
+                  el: node as HTMLElement,
+                  schema,
+                }) ??
+                  DOMParser.fromSchema(schema).parse(node as HTMLElement, {
+                    topNode: schema.nodes["blockGroup"].create(),
+                    preserveWhitespace: true,
+                  }).content,
+                schema,
+                config.content !== "none",
+              )
+          : undefined
+        : config.content === "inline" ||
+            config.content === "none" ||
+            config.content === "plain"
           ? (node, schema) => {
               if (implementation.parseContent) {
                 const result = implementation.parseContent({
@@ -167,130 +256,425 @@ export function getParseRules<
   return rules;
 }
 
-// A function to create custom block for API consumers
-// we want to hide the tiptap node from API consumers and provide a simpler API surface instead
-export function addNodeAndExtensionsToSpec<
+function buildContainerNode<TName extends string, TProps extends PropSchema>(
+  blockConfig: BlockConfig<TName, TProps, "none">,
+  blockImplementation: BlockImplementation<TName, TProps, "none">,
+  schemaContext: BlockSchemaContext,
+  priority?: number,
+) {
+  const children = getChildrenConfig(blockConfig)!;
+
+  const groups = ["bnBlock", "childContainer"];
+  if (isPlaceableAnywhere(blockConfig)) {
+    groups.push("blockGroupChild");
+  }
+
+  return Node.create({
+    name: blockConfig.type,
+    content: childrenContentExpression(children, schemaContext),
+    group: groups.join(" "),
+    marks() {
+      return suggestionMarks(this.editor);
+    },
+    selectable: blockImplementation.meta?.selectable ?? true,
+    isolating: blockImplementation.meta?.isolating ?? true,
+    defining: true,
+    priority: containerNodePriority(priority),
+    addAttributes() {
+      return propsToAttributes(blockConfig.propSchema);
+    },
+
+    parseHTML() {
+      return getParseRules(blockConfig, blockImplementation, "container");
+    },
+
+    renderHTML({ HTMLAttributes }) {
+      const dom = document.createElement("div");
+      dom.setAttribute("data-node-type", blockConfig.type);
+      for (const [attribute, value] of Object.entries(HTMLAttributes)) {
+        dom.setAttribute(attribute, value as string);
+      }
+      return { dom, contentDOM: dom };
+    },
+
+    addNodeView() {
+      return (props) =>
+        containerNodeView(blockConfig, blockImplementation, props, {
+          editor: this.options.editor,
+          tiptapEditor: this.editor,
+          blockContentDOMAttributes:
+            this.options.domAttributes?.blockContent || {},
+        });
+    },
+  });
+}
+
+function containerRootDOM(output: {
+  dom: HTMLElement | DocumentFragment;
+  rootDOM?: HTMLElement | null;
+}): HTMLElement | DocumentFragment | null | undefined {
+  return output.rootDOM === undefined ? output.dom : output.rootDOM;
+}
+
+function containerNodeView<
+  TName extends string,
+  TProps extends PropSchema,
+  TContent extends "inline" | "none" | "plain",
+>(
+  blockConfig: BlockConfig<TName, TProps, TContent>,
+  blockImplementation: BlockImplementation<TName, TProps, TContent>,
+  props: NodeViewRendererProps,
+  context: {
+    editor: unknown;
+    tiptapEditor: Editor;
+    blockContentDOMAttributes: Record<string, string>;
+  },
+): NodeView {
+  const block = nodeToBlock(props.node, props.view.state.doc);
+
+  const nodeView = blockImplementation.render.call(
+    {
+      blockContentDOMAttributes: context.blockContentDOMAttributes,
+      props,
+      renderType: "nodeView",
+      propSchema: blockConfig.propSchema,
+    },
+    block as any,
+    context.editor as any,
+  );
+
+  const rootDOM = () => containerRootDOM(nodeView);
+
+  applyContainerAttributes(
+    rootDOM(),
+    blockConfig.type,
+    block.props as any,
+    blockConfig.propSchema,
+    block.id,
+  );
+
+  const typedNodeView = nodeView as unknown as NodeView;
+
+  if (blockImplementation.meta?.selectable === false) {
+    applyNonSelectableBlockFix(typedNodeView, context.tiptapEditor);
+  }
+
+  ignoreNonContentMutations(typedNodeView);
+
+  const update = typedNodeView.update?.bind(typedNodeView);
+  if (update) {
+    typedNodeView.update = (node, decorations, innerDecorations) => {
+      if (node.type.name !== blockConfig.type) {
+        return false;
+      }
+      if (update(node, decorations, innerDecorations) === false) {
+        return false;
+      }
+      applyContainerAttributes(
+        rootDOM(),
+        blockConfig.type,
+        nodeToBlock(node, props.view.state.doc).props as any,
+        blockConfig.propSchema,
+        node.attrs.id,
+      );
+      return true;
+    };
+  }
+
+  return typedNodeView;
+}
+
+function buildContentContainerNode<
+  TName extends string,
+  TProps extends PropSchema,
+  TContent extends "inline" | "plain",
+>(
+  blockConfig: BlockConfig<TName, TProps, TContent>,
+  blockImplementation: BlockImplementation<TName, TProps, TContent>,
+  schemaContext: BlockSchemaContext,
+  priority?: number,
+): { node: Node; extraNodes: Node[] } {
+  const children = getChildrenConfig(blockConfig)!;
+
+  const contentName = containerContentNodeName(blockConfig.type);
+  const childrenName = containerChildrenNodeName(blockConfig.type);
+  const nodePriority = containerNodePriority(priority);
+
+  const groups = ["bnBlock"];
+  if (isPlaceableAnywhere(blockConfig)) {
+    groups.push("blockGroupChild");
+  }
+
+  const node = Node.create({
+    name: blockConfig.type,
+    content: `${contentName} ${childrenName}`,
+    group: groups.join(" "),
+    marks() {
+      return suggestionMarks(this.editor);
+    },
+    selectable: blockImplementation.meta?.selectable ?? true,
+    isolating: blockImplementation.meta?.isolating ?? true,
+    defining: true,
+    priority: nodePriority,
+    addAttributes() {
+      return propsToAttributes(blockConfig.propSchema);
+    },
+
+    parseHTML() {
+      return getParseRules(blockConfig, blockImplementation, "container");
+    },
+
+    renderHTML({ HTMLAttributes }) {
+      const dom = document.createElement("div");
+      dom.setAttribute("data-node-type", blockConfig.type);
+      for (const [attribute, value] of Object.entries(HTMLAttributes)) {
+        dom.setAttribute(attribute, value as string);
+      }
+      return { dom, contentDOM: dom };
+    },
+
+    addNodeView() {
+      return (props) =>
+        containerNodeView(blockConfig, blockImplementation, props, {
+          editor: this.options.editor,
+          tiptapEditor: this.editor,
+          blockContentDOMAttributes:
+            this.options.domAttributes?.blockContent || {},
+        });
+    },
+  });
+
+  const contentNode = Node.create({
+    name: contentName,
+    group: CONTAINER_CONTENT_GROUP,
+    content: blockConfig.content === "plain" ? "text*" : "inline*",
+    marks() {
+      return blockConfig.content === "plain"
+        ? nonFormattingMarks(this.editor)
+        : undefined;
+    },
+    code: blockImplementation.meta?.code ?? false,
+    defining: true,
+    priority: nodePriority,
+
+    parseHTML() {
+      return [{ tag: `[data-content-type=${blockConfig.type}]` }];
+    },
+
+    renderHTML() {
+      const dom = document.createElement("div");
+      dom.className = "bn-inline-content";
+      dom.setAttribute("data-content-type", blockConfig.type);
+      return { dom, contentDOM: dom };
+    },
+  });
+
+  const childrenNode = Node.create({
+    name: childrenName,
+    group: CHILD_CONTAINER_GROUP,
+    content: childrenContentExpression(children, schemaContext),
+    marks() {
+      return suggestionMarks(this.editor);
+    },
+    priority: nodePriority,
+
+    parseHTML() {
+      return [{ tag: `[data-children-of=${blockConfig.type}]` }];
+    },
+
+    renderHTML() {
+      const dom = document.createElement("div");
+      dom.setAttribute("data-children-of", blockConfig.type);
+      return { dom, contentDOM: dom };
+    },
+  });
+
+  return { node, extraNodes: [contentNode, childrenNode] };
+}
+
+function buildRegularNode<
   TName extends string,
   TProps extends PropSchema,
   TContent extends "inline" | "none" | "table" | "plain",
 >(
   blockConfig: BlockConfig<TName, TProps, TContent>,
   blockImplementation: BlockImplementation<TName, TProps, TContent>,
-  extensions?: (ExtensionFactoryInstance | Extension)[],
   priority?: number,
-): LooseBlockSpec<TName, TProps, TContent> {
-  const node =
-    ((blockImplementation as any).node as Node) ||
-    Node.create({
-      name: blockConfig.type,
-      content: (blockConfig.content === "inline"
-        ? "inline*"
-        : blockConfig.content === "plain"
-          ? "text*"
-          : blockConfig.content === "none"
-            ? ""
-            : blockConfig.content) as TContent extends "inline"
-        ? "inline*"
-        : TContent extends "plain"
-          ? "text*"
-          : "",
-      // "plain" blocks hold unstyled text, so they disallow formatting marks.
-      // They still allow the non-formatting marks (comments and
-      // suggestions/diffs) — those annotate content without changing it and are
-      // ignored by the block model. `nonFormattingMarks` resolves the group only
-      // when at least one such mark is registered, so a plain block in an editor
-      // without any of them doesn't reference an empty (unknown) mark group.
-      marks() {
-        return blockConfig.content === "plain"
-          ? nonFormattingMarks(this.editor)
-          : undefined;
-      },
-      group: "blockContent",
-      selectable: blockImplementation.meta?.selectable ?? true,
-      isolating: blockImplementation.meta?.isolating ?? true,
-      code: blockImplementation.meta?.code ?? false,
-      defining: blockImplementation.meta?.defining ?? true,
-      priority,
-      addAttributes() {
-        return propsToAttributes(blockConfig.propSchema);
-      },
+) {
+  return Node.create({
+    name: blockConfig.type,
+    content: (blockConfig.content === "inline"
+      ? "inline*"
+      : blockConfig.content === "plain"
+        ? "text*"
+        : blockConfig.content === "none"
+          ? ""
+          : blockConfig.content) as TContent extends "inline"
+      ? "inline*"
+      : TContent extends "plain"
+        ? "text*"
+        : "",
+    // "plain" blocks hold unstyled text, so they disallow formatting marks.
+    // They still allow the non-formatting marks (comments and
+    // suggestions/diffs) — those annotate content without changing it and are
+    // ignored by the block model. `nonFormattingMarks` resolves the group only
+    // when at least one such mark is registered, so a plain block in an editor
+    // without any of them doesn't reference an empty (unknown) mark group.
+    marks() {
+      return blockConfig.content === "plain"
+        ? nonFormattingMarks(this.editor)
+        : undefined;
+    },
+    group: "blockContent",
+    selectable: blockImplementation.meta?.selectable ?? true,
+    isolating: blockImplementation.meta?.isolating ?? true,
+    code: blockImplementation.meta?.code ?? false,
+    defining: blockImplementation.meta?.defining ?? true,
+    priority,
+    addAttributes() {
+      return propsToAttributes(blockConfig.propSchema);
+    },
 
-      parseHTML() {
-        return getParseRules(blockConfig, blockImplementation);
-      },
+    parseHTML() {
+      return getParseRules(blockConfig, blockImplementation);
+    },
+
+    renderHTML({ HTMLAttributes }) {
+      // renderHTML is used for copy/pasting content from the editor back into
+      // the editor, so we need to make sure the `blockContent` element is
+      // structured correctly as this is what's used for parsing blocks. We
+      // just render a placeholder div inside as the `blockContent` element
+      // already has all the information needed for proper parsing.
+      const div = document.createElement("div");
+      return wrapInBlockStructure(
+        {
+          dom: div,
+          contentDOM:
+            blockConfig.content === "inline" || blockConfig.content === "plain"
+              ? div
+              : undefined,
+        },
+        blockConfig.type,
+        {},
+        blockConfig.propSchema,
+        blockImplementation.meta?.fileBlockAccept !== undefined,
+        HTMLAttributes,
+      );
+    },
+
+    addNodeView() {
+      return (props) => {
+        // Gets the BlockNote editor instance
+        const editor = this.options.editor;
+        // Gets the block. Resolving this can't rely on `getPos()` alone —
+        // node views are constructed part-way through ProseMirror's
+        // reconciliation, where positions don't always line up with
+        // `view.state.doc` yet (see `getBlockFromNodeView`).
+        const block = getBlockFromNodeView(
+          props.getPos,
+          props.node,
+          props.view.state.doc,
+        );
+        // Gets the custom HTML attributes for `blockContent` nodes
+        const blockContentDOMAttributes =
+          this.options.domAttributes?.blockContent || {};
 
-      renderHTML({ HTMLAttributes }) {
-        // renderHTML is used for copy/pasting content from the editor back into
-        // the editor, so we need to make sure the `blockContent` element is
-        // structured correctly as this is what's used for parsing blocks. We
-        // just render a placeholder div inside as the `blockContent` element
-        // already has all the information needed for proper parsing.
-        const div = document.createElement("div");
-        return wrapInBlockStructure(
+        const nodeView = blockImplementation.render.call(
           {
-            dom: div,
-            contentDOM:
-              blockConfig.content === "inline" ||
-              blockConfig.content === "plain"
-                ? div
-                : undefined,
+            blockContentDOMAttributes,
+            props,
+            renderType: "nodeView",
+            propSchema: blockConfig.propSchema,
           },
-          blockConfig.type,
-          {},
-          blockConfig.propSchema,
-          blockImplementation.meta?.fileBlockAccept !== undefined,
-          HTMLAttributes,
+          block as any,
+          editor as any,
         );
-      },
 
-      addNodeView() {
-        return (props) => {
-          // Gets the BlockNote editor instance
-          const editor = this.options.editor;
-          // Gets the block. Resolving this can't rely on `getPos()` alone —
-          // node views are constructed part-way through ProseMirror's
-          // reconciliation, where positions don't always line up with
-          // `view.state.doc` yet (see `getBlockFromNodeView`).
-          const block = getBlockFromNodeView(
-            props.getPos,
-            props.node,
-            props.view.state.doc,
-          );
-          // Gets the custom HTML attributes for `blockContent` nodes
-          const blockContentDOMAttributes =
-            this.options.domAttributes?.blockContent || {};
+        // Cast needed because render returns `dom: HTMLElement | DocumentFragment`
+        // but tiptap's NodeView expects `dom: HTMLElement`
+        const typedNodeView = nodeView as unknown as NodeView;
 
-          const nodeView = blockImplementation.render.call(
-            {
-              blockContentDOMAttributes,
-              props,
-              renderType: "nodeView",
-              propSchema: blockConfig.propSchema,
-            },
-            block as any,
-            editor as any,
-          );
+        if (blockImplementation.meta?.selectable === false) {
+          applyNonSelectableBlockFix(typedNodeView, this.editor);
+        }
 
-          // Cast needed because render returns `dom: HTMLElement | DocumentFragment`
-          // but tiptap's NodeView expects `dom: HTMLElement`
-          const typedNodeView = nodeView as unknown as NodeView;
+        // Ignores DOM mutations that don't affect the block's content, so
+        // that browser extensions which rewrite the DOM (e.g. Dark Reader)
+        // can't trigger an infinite re-render loop that freezes the tab.
+        ignoreNonContentMutations(typedNodeView);
+
+        // See explanation for why `update` is not implemented for NodeViews
+        // https://github.com/TypeCellOS/BlockNote/pull/1904#discussion_r2313461464
+        // TODO: in a future version, we might want to implement updates so that
+        // vanilla blocks don't always re-render entirely (https://github.com/TypeCellOS/BlockNote/issues/220)
+        return typedNodeView;
+      };
+    },
+  });
+}
 
-          if (blockImplementation.meta?.selectable === false) {
-            applyNonSelectableBlockFix(typedNodeView, this.editor);
-          }
+// A function to create custom block for API consumers
+// we want to hide the tiptap node from API consumers and provide a simpler API surface instead
+export function addNodeAndExtensionsToSpec<
+  TName extends string,
+  TProps extends PropSchema,
+  TContent extends "inline" | "none" | "table" | "plain",
+>(
+  blockConfig: BlockConfig<TName, TProps, TContent>,
+  blockImplementation: BlockImplementation<TName, TProps, TContent>,
+  extensions?: (ExtensionFactoryInstance | Extension)[],
+  priority?: number,
+  schemaContext: BlockSchemaContext = NO_SCHEMA_CONTEXT,
+): LooseBlockSpec<TName, TProps, TContent> {
+  const childrenConfig = getChildrenConfig(blockConfig);
 
-          // Ignores DOM mutations that don't affect the block's content, so
-          // that browser extensions which rewrite the DOM (e.g. Dark Reader)
-          // can't trigger an infinite re-render loop that freezes the tab.
-          ignoreNonContentMutations(typedNodeView);
+  if (childrenConfig && blockConfig.content === "table") {
+    throw new Error(
+      `Block "${blockConfig.type}" sets \`children\` but its \`content\` is "table". A table block cannot also hold child blocks.`,
+    );
+  }
 
-          // See explanation for why `update` is not implemented for NodeViews
-          // https://github.com/TypeCellOS/BlockNote/pull/1904#discussion_r2313461464
-          // https://github.com/TypeCellOS/BlockNote/issues/220
-          return typedNodeView;
-        };
-      },
-    });
+  const isContainer = childrenConfig !== undefined;
+
+  // A container with its own content is built from three nodes (see
+  // `buildContentContainerNode`); every other kind of block is a single node.
+  const built: { node: Node; extraNodes?: Node[] } = (
+    blockImplementation as any
+  ).node
+    ? { node: (blockImplementation as any).node as Node }
+    : childrenConfig && blockConfig.content !== "none"
+      ? buildContentContainerNode(
+          blockConfig as unknown as BlockConfig<
+            TName,
+            TProps,
+            "inline" | "plain"
+          >,
+          blockImplementation as unknown as BlockImplementation<
+            TName,
+            TProps,
+            "inline" | "plain"
+          >,
+          schemaContext,
+          priority,
+        )
+      : childrenConfig
+        ? {
+            node: buildContainerNode(
+              blockConfig as unknown as BlockConfig<TName, TProps, "none">,
+              blockImplementation as unknown as BlockImplementation<
+                TName,
+                TProps,
+                "none"
+              >,
+              schemaContext,
+              priority,
+            ),
+          }
+        : {
+            node: buildRegularNode(blockConfig, blockImplementation, priority),
+          };
+
+  const { node, extraNodes } = built;
 
   if (node.name !== blockConfig.type) {
     throw new Error(
@@ -303,11 +687,12 @@ export function addNodeAndExtensionsToSpec<
     implementation: {
       ...blockImplementation,
       node,
+      ...(extraNodes ? { extraNodes } : {}),
       render(block, editor) {
         const blockContentDOMAttributes =
           node.options.domAttributes?.blockContent || {};
 
-        return blockImplementation.render.call(
+        const output = blockImplementation.render.call(
           {
             blockContentDOMAttributes,
             props: undefined,
@@ -317,6 +702,18 @@ export function addNodeAndExtensionsToSpec<
           block as any,
           editor as any,
         );
+
+        if (isContainer) {
+          applyContainerAttributes(
+            containerRootDOM(output),
+            blockConfig.type,
+            block.props as any,
+            blockConfig.propSchema,
+            block.id,
+          );
+        }
+
+        return output;
       },
       // TODO: this should not have wrapInBlockStructure and generally be a lot simpler
       // post-processing in externalHTMLExporter should not be necessary
@@ -324,7 +721,7 @@ export function addNodeAndExtensionsToSpec<
         const blockContentDOMAttributes =
           node.options.domAttributes?.blockContent || {};
 
-        return (
+        const output =
           blockImplementation.toExternalHTML?.call(
             { blockContentDOMAttributes, propSchema: blockConfig.propSchema },
             block as any,
@@ -340,8 +737,19 @@ export function addNodeAndExtensionsToSpec<
             },
             block as any,
             editor as any,
-          )
-        );
+          );
+
+        if (output && isContainer) {
+          applyContainerAttributes(
+            containerRootDOM(output),
+            blockConfig.type,
+            block.props as any,
+            blockConfig.propSchema,
+            block.id,
+          );
+        }
+
+        return output;
       },
     },
     extensions,
@@ -452,6 +860,8 @@ export function createBlockSpec<
         : extensionsOrCreator
       : undefined;
 
+    const isContainer = getChildrenConfig(blockConfig) !== undefined;
+
     return {
       config: blockConfig,
       implementation: {
@@ -470,6 +880,11 @@ export function createBlockSpec<
             return undefined;
           }
 
+          if (isContainer) {
+            applyDOMAttributes(output.dom, this.blockContentDOMAttributes);
+            return output;
+          }
+
           return wrapInBlockStructure(
             output,
             block.type,
@@ -489,6 +904,11 @@ export function createBlockSpec<
             editor as any,
           );
 
+          if (isContainer) {
+            applyDOMAttributes(output.dom, this.blockContentDOMAttributes);
+            return output;
+          }
+
           const nodeView = wrapInBlockStructure(
             output,
             block.type,
diff --git a/packages/core/src/schema/blocks/internal.ts b/packages/core/src/schema/blocks/internal.ts
index cfd17b9d11..551963f417 100644
--- a/packages/core/src/schema/blocks/internal.ts
+++ b/packages/core/src/schema/blocks/internal.ts
@@ -6,7 +6,7 @@ import type { ExtensionFactoryInstance } from "../../editor/BlockNoteExtension.j
 import { mergeCSSClasses } from "../../util/browser.js";
 import { camelToDataKebab } from "../../util/string.js";
 import { PropSchema, Props } from "../propTypes.js";
-import { LooseBlockSpec } from "./types.js";
+import { BlockConfig, ChildrenConfig, LooseBlockSpec } from "./types.js";
 
 // Function that uses the 'propSchema' of a blockConfig to create a TipTap
 // node's `addAttributes` property.
@@ -157,6 +157,26 @@ export function getBlockFromNodeView(
   }
 }
 
+/**
+ * Applies custom `blockContent` DOM attributes to an element, merging (rather
+ * than overwriting) its class list.
+ */
+export function applyDOMAttributes(
+  dom: HTMLElement | DocumentFragment,
+  domAttributes: Record<string, string> | undefined,
+) {
+  if (!domAttributes || !(dom instanceof HTMLElement)) {
+    return;
+  }
+  for (const [attr, value] of Object.entries(domAttributes)) {
+    if (attr === "class") {
+      dom.className = mergeCSSClasses(dom.className, value);
+    } else {
+      dom.setAttribute(attr, value);
+    }
+  }
+}
+
 // Function that wraps the `dom` element returned from 'blockConfig.render' in a
 // `blockContent` div, which contains the block type and props as HTML
 // attributes. If `blockConfig.render` also returns a `contentDOM`, it also adds
@@ -232,6 +252,12 @@ export function createBlockSpecFromTiptapNode<
     node: Node;
     type: string;
     content: "inline" | "table" | "none" | "plain";
+    // Declares the block's container semantics (child counts/repair etc.) even
+    // though the node itself is hand-written — the node's own content
+    // expression stays authoritative for the PM schema, while BlockNote-level
+    // behavior (repair, seeding, validation) reads this config.
+    children?: ChildrenConfig;
+    placement?: BlockConfig["placement"];
   },
   P extends PropSchema,
 >(
@@ -244,6 +270,10 @@ export function createBlockSpecFromTiptapNode<
       type: config.type as T["type"],
       content: config.content,
       propSchema,
+      ...(config.children !== undefined ? { children: config.children } : {}),
+      ...(config.placement !== undefined
+        ? { placement: config.placement }
+        : {}),
     },
     implementation: {
       node: config.node,
diff --git a/packages/core/src/schema/blocks/types.ts b/packages/core/src/schema/blocks/types.ts
index 8d7e203e61..82e9d60ebb 100644
--- a/packages/core/src/schema/blocks/types.ts
+++ b/packages/core/src/schema/blocks/types.ts
@@ -1,11 +1,7 @@
 /** Define the main block types **/
 // import { Extension, Node } from "@tiptap/core";
 import type { Node, NodeViewRendererProps } from "@tiptap/core";
-import type {
-  Fragment,
-  Node as ProsemirrorNode,
-  Schema,
-} from "prosemirror-model";
+import type { Fragment, Node as PMNode, Schema } from "prosemirror-model";
 import type { ViewMutationRecord } from "prosemirror-view";
 import type { BlockNoteEditor } from "../../editor/BlockNoteEditor.js";
 import type {
@@ -67,6 +63,16 @@ export interface BlockConfigMeta<
    */
   isolating?: boolean;
 
+  /**
+   * Whether this block type gets a side menu drag handle (and can be dragged
+   * by it). Applies to any block type, not just container blocks — e.g. a
+   * "locked" block can opt out of dragging entirely. A block that opts out is
+   * skipped when looking for a drag handle, so the handle falls through to the
+   * nearest draggable ancestor.
+   * @default true
+   */
+  draggable?: boolean;
+
   /**
    * Enables syntax highlighting of the contents of the block with the result of this callback
    */
@@ -80,6 +86,118 @@ export interface BlockConfigMeta<
   hasPreview?: boolean;
 }
 
+/**
+ * What may appear in one child position of a container block.
+ *
+ * The two fields mirror the only two distinctions the document schema can
+ * make. Every regular block is the *same* ProseMirror node (`blockContainer`),
+ * so "only headings" is not expressible — and therefore is not offered.
+ * Container-type blocks are their own node type, so those are exact.
+ */
+export type ChildrenAllow = {
+  /**
+   * Whether regular (non-container) blocks are allowed. This cannot be
+   * narrowed to specific block types: paragraphs, headings and code blocks are
+   * indistinguishable at the node level.
+   * @default true
+   */
+  blocks?: boolean;
+  /**
+   * Which container-block types are allowed. `true` for any container type,
+   * `false` for none, or an explicit list — enforced exactly by the schema.
+   * @default true
+   */
+  containers?: boolean | readonly string[];
+};
+
+/** How many children fill one slot. A bare number means exactly that many. */
+export type ChildCount = number | { min?: number; max?: number };
+
+/** One position in an ordered {@link ChildrenConfig.sequence}. */
+export type ChildSlot = {
+  allow?: ChildrenAllow;
+  /** @default 1 — a slot names a position, so it holds one child unless told otherwise. */
+  count?: ChildCount;
+};
+
+type ChildrenBehavior = {
+  /**
+   * Children to create the container with when it is inserted without an
+   * explicit `children` array. When omitted, BlockNote fills the container
+   * with whatever its content expression requires (usually one empty
+   * paragraph), so a container can never be created in an invalid state.
+   */
+  default?: readonly PartialBlockNoDefaults<any, any, any>[];
+  /**
+   * As children are emptied out (Backspace merges the last child away,
+   * `replaceBlocks` deletes children, ...), drop the emptied children and —
+   * when fewer than the required number of non-empty children remain —
+   * replace the container with its survivors, or remove it entirely when none
+   * remain. Column lists use this so emptied columns disappear and a
+   * one-column list unwraps.
+   *
+   * Coupled to the child count, so it lives here rather than in `meta`:
+   * without it repair is a no-op, because ProseMirror's schema fitting always
+   * pads a container back up to its minimum with empty children, so
+   * "effectively below the minimum" can only be detected by discounting those.
+   * @default false
+   */
+  unwrapWhenEmptied?: boolean;
+  /**
+   * Whether pressing Enter on an empty block that is the last child of this
+   * container moves that block out of (after) the container, list-style.
+   * Without it, a container as the last block in the document can trap the
+   * cursor, as Enter only ever creates new blocks *within* the container.
+   * @default true
+   */
+  exitOnEnter?: boolean;
+};
+
+/**
+ * Marks a block as a *container*: a block whose body is other blocks, exposed
+ * as `block.children` at runtime.
+ *
+ * Two forms — a uniform body (`allow` plus `min`/`max`), or an ordered body
+ * (`sequence`). The uniform form is exactly sugar for a one-slot sequence.
+ */
+export type ChildrenConfig = ChildrenBehavior &
+  (
+    | {
+        allow?: ChildrenAllow;
+        /** @default 1 */
+        min?: number;
+        /** @default unbounded */
+        max?: number;
+        sequence?: never;
+      }
+    | {
+        sequence: readonly ChildSlot[];
+        allow?: never;
+        min?: never;
+        max?: never;
+      }
+  );
+
+/** One slot of a {@link ChildrenConfig}, with every default filled in. */
+export type ResolvedSlot = {
+  blocks: boolean;
+  /** `true` for any container type; a (possibly empty) list otherwise. */
+  containers: true | readonly string[];
+  min: number;
+  max: number | undefined;
+};
+
+/** A {@link ChildrenConfig} with every default filled in. */
+export type ResolvedChildren = {
+  slots: ResolvedSlot[];
+  /** Sum of the slots' minimums — what `unwrapWhenEmptied` compares against. */
+  minCount: number;
+  maxCount: number | undefined;
+  default: readonly PartialBlockNoDefaults<any, any, any>[] | undefined;
+  unwrapWhenEmptied: boolean;
+  exitOnEnter: boolean;
+};
+
 /**
  * BlockConfig contains the "schema" info about a Block type
  * i.e. what props it supports, what content it supports, etc.
@@ -106,8 +224,31 @@ export interface BlockConfig<
    * The content that the block supports
    */
   content: C;
-  // TODO: how do you represent things that have nested content?
-  // e.g. tables, alerts (with title & content)
+  /**
+   * Makes this a *container* block: a block whose body is other blocks,
+   * exposed on `block.children`. The block's `render` places them via
+   * `contentRef` (React) / `contentDOM` (vanilla), the same way it would place
+   * inline content.
+   *
+   * Can be combined with `content: "inline"` / `"plain"`, in which case the
+   * block has its own content *and* children, and both are placed in that one
+   * editable region. Only `content: "table"` is incompatible.
+   *
+   * `children: {}` is the minimal container.
+   */
+  children?: ChildrenConfig;
+  /**
+   * Where this block may be placed.
+   *
+   * - `"anywhere"` (default): anywhere a regular block goes — the document
+   *   root, or nested under any other block.
+   * - `"containerOnly"`: only inside a container that names this type in its
+   *   `children.allow.containers` (e.g. a `column` inside a `columnList`).
+   *
+   * Only meaningful for container blocks; regular blocks are always placeable
+   * anywhere.
+   */
+  placement?: "anywhere" | "containerOnly";
 }
 
 /**
@@ -227,9 +368,11 @@ export type LooseBlockSpec<
     ) => {
       dom: HTMLElement | DocumentFragment;
       contentDOM?: HTMLElement;
+      /** See {@link BlockImplementation.render}'s `rootDOM`. */
+      rootDOM?: HTMLElement | null;
       ignoreMutation?: (mutation: ViewMutationRecord) => boolean;
-      update?: (node: ProsemirrorNode) => boolean;
       destroy?: () => void;
+      update?: (node: PMNode) => boolean | void;
     };
     toExternalHTML?: (
       block: any,
@@ -246,6 +389,12 @@ export type LooseBlockSpec<
       | undefined;
 
     node: Node;
+    /**
+     * Nodes the block's own node needs in the schema but which aren't blocks
+     * themselves — the generated content & children nodes of a container block
+     * that has its own content. Registered alongside `node`.
+     */
+    extraNodes?: Node[];
   };
   extensions?: (Extension | ExtensionFactoryInstance)[];
 };
@@ -286,9 +435,11 @@ export type BlockSpecs = {
       ) => {
         dom: HTMLElement | DocumentFragment;
         contentDOM?: HTMLElement;
+        /** See {@link BlockImplementation.render}'s `rootDOM`. */
+        rootDOM?: HTMLElement | null;
         ignoreMutation?: (mutation: ViewMutationRecord) => boolean;
-        update?: (node: ProsemirrorNode) => boolean;
         destroy?: () => void;
+        update?: (node: PMNode) => boolean | void;
       };
       toExternalHTML?: (
         block: any,
@@ -590,19 +741,31 @@ export type BlockImplementation<
   ) => {
     dom: HTMLElement | DocumentFragment;
     contentDOM?: HTMLElement;
+    /**
+     * The block author's own root element, when it isn't `dom` itself. React
+     * renders a node view through wrapper elements of its own, so the element
+     * ProseMirror is handed is not the one the author wrote — this points at
+     * the latter, and is what container attributes (`data-node-type`,
+     * `data-id`, prop `data-*`) are stamped onto.
+     * @default dom
+     */
+    rootDOM?: HTMLElement | null;
     ignoreMutation?: (mutation: ViewMutationRecord) => boolean;
+    destroy?: () => void;
     /**
-     * Called by ProseMirror when this block's node is updated (e.g. its content
-     * or props change). Return `true` to handle the update in place - keeping
-     * the existing DOM - or `false` to have the node view recreated via
-     * `render`. When omitted, ProseMirror keeps the node view and reconciles its
-     * `contentDOM` in place as long as the node type stays the same.
+     * Optional NodeView update hook. Called when the underlying ProseMirror
+     * node's attributes change (or its decorations change). Return `false` to
+     * tell ProseMirror to destroy and recreate the NodeView (i.e. re-run
+     * `render` from scratch). Return `true` (or `undefined`) when you have
+     * patched `dom` in-place and PM should keep the existing view.
      *
-     * Useful for blocks whose `render` builds custom DOM that needs to stay in
-     * sync with the node (e.g. a code block rendering a preview of its content).
+     * Only honored for container blocks (blocks with `children`), where
+     * recreating the node view would remount every child block — e.g. column
+     * resizing patches widths in place through this hook. Non-container
+     * blocks always recreate on attr changes (see
+     * https://github.com/TypeCellOS/BlockNote/pull/1904#discussion_r2313461464).
      */
-    update?: (node: ProsemirrorNode) => boolean;
-    destroy?: () => void;
+    update?: (node: PMNode) => boolean | void;
   };
 
   /**
diff --git a/packages/core/src/schema/blocks/validateChildren.test.ts b/packages/core/src/schema/blocks/validateChildren.test.ts
new file mode 100644
index 0000000000..f60bdf16eb
--- /dev/null
+++ b/packages/core/src/schema/blocks/validateChildren.test.ts
@@ -0,0 +1,252 @@
+// @vitest-environment node
+import { describe, expect, it } from "vite-plus/test";
+
+import type { ChildrenConfig } from "./types.js";
+import { validateChildrenConfigs } from "./validateChildren.js";
+
+type ContainerFixture = {
+  children: ChildrenConfig;
+  placement?: "anywhere" | "containerOnly";
+};
+
+function configsWith(containers: Record<string, ContainerFixture>) {
+  return {
+    paragraph: { type: "paragraph", content: "inline" as const },
+    heading: { type: "heading", content: "inline" as const },
+    ...Object.fromEntries(
+      Object.entries(containers).map(([type, { children, placement }]) => [
+        type,
+        { type, content: "none" as const, children, placement },
+      ]),
+    ),
+  };
+}
+
+const validate = (containers: Record<string, ContainerFixture>) => () =>
+  validateChildrenConfigs(configsWith(containers));
+
+describe("validateChildrenConfigs", () => {
+  it("accepts a plain container config", () => {
+    expect(validate({ callout: { children: { min: 1 } } })).not.toThrow();
+  });
+
+  it("accepts the columnList shape (restricted children, min 2)", () => {
+    expect(
+      validate({
+        grid: {
+          children: {
+            allow: { blocks: false, containers: ["gridCell"] },
+            min: 2,
+          },
+        },
+        gridCell: { children: {}, placement: "containerOnly" },
+      }),
+    ).not.toThrow();
+  });
+
+  it("rejects unknown allow.containers entries", () => {
+    expect(
+      validate({ grid: { children: { allow: { containers: ["nope"] } } } }),
+    ).toThrow(/nope/);
+  });
+
+  // The bug this redesign exists to fix: `allowedBlocks: ["heading"]` used to
+  // compile to "any regular block" and validate as if it had restricted
+  // something. Naming a regular type is now a hard error rather than a lie.
+  it("rejects a regular block type in allow.containers", () => {
+    expect(
+      validate({ grid: { children: { allow: { containers: ["heading"] } } } }),
+    ).toThrow(/regular block, not a container block/);
+  });
+
+  it("rejects an allow that permits nothing", () => {
+    expect(
+      validate({
+        grid: { children: { allow: { blocks: false, containers: false } } },
+      }),
+    ).toThrow(/permits nothing/);
+  });
+
+  it("rejects container-only allow when the schema has no other containers", () => {
+    expect(
+      validate({
+        grid: { children: { allow: { blocks: false, containers: true } } },
+      }),
+    ).toThrow(/no other container block types/);
+  });
+
+  it("rejects negative or non-integer minimums", () => {
+    expect(validate({ callout: { children: { min: -1 } } })).toThrow(
+      /non-negative integer/,
+    );
+  });
+
+  it("rejects a maximum smaller than the minimum", () => {
+    expect(validate({ callout: { children: { min: 3, max: 2 } } })).toThrow(
+      /greater than or equal/,
+    );
+  });
+
+  it("rejects an empty sequence", () => {
+    expect(validate({ card: { children: { sequence: [] } } })).toThrow(
+      /must not be empty/,
+    );
+  });
+
+  it("rejects `default` violating the child count", () => {
+    expect(
+      validate({
+        callout: { children: { min: 2, default: [{ type: "paragraph" }] } },
+      }),
+    ).toThrow(/fewer than the 2 required/);
+  });
+
+  it("rejects `default` containing a block the slot doesn't permit", () => {
+    expect(
+      validate({
+        grid: {
+          children: {
+            allow: { blocks: false, containers: ["gridCell"] },
+            min: 2,
+            default: [{ type: "paragraph" }, { type: "paragraph" }],
+          },
+        },
+        gridCell: { children: {}, placement: "containerOnly" },
+      }),
+    ).toThrow(/not permitted/);
+  });
+
+  it("reports which sequence slot rejected a `default` entry", () => {
+    expect(
+      validate({
+        card: {
+          children: {
+            sequence: [
+              { allow: { blocks: false, containers: ["cardHeader"] } },
+              { allow: { containers: false }, count: { min: 1 } },
+            ],
+            default: [{ type: "paragraph" }, { type: "paragraph" }],
+          },
+        },
+        cardHeader: { children: {}, placement: "containerOnly" },
+      }),
+    ).toThrow(/`sequence` slot 0/);
+  });
+
+  // A `default` may legitimately skip a leading optional slot whose `min` is
+  // already met — the walker must move past it rather than forcing the child
+  // into a slot that doesn't accept it.
+  it("accepts a `default` that skips a leading optional slot", () => {
+    expect(
+      validate({
+        card: {
+          children: {
+            sequence: [
+              {
+                allow: { blocks: false, containers: ["cardHeader"] },
+                count: { min: 0, max: 1 },
+              },
+              { allow: { blocks: true }, count: { min: 1 } },
+            ],
+            default: [{ type: "paragraph" }],
+          },
+        },
+        cardHeader: { children: {}, placement: "containerOnly" },
+      }),
+    ).not.toThrow();
+  });
+
+  it("rejects placement on a block that isn't a container", () => {
+    expect(() =>
+      validateChildrenConfigs({
+        paragraph: {
+          type: "paragraph",
+          content: "inline",
+          placement: "containerOnly",
+        },
+      }),
+    ).toThrow(/only applies to container blocks/);
+  });
+
+  it("rejects a containerOnly block no container accepts", () => {
+    expect(
+      validate({
+        grid: {
+          children: {
+            allow: { blocks: false, containers: ["gridCell"] },
+            min: 2,
+          },
+        },
+        gridCell: {
+          children: { allow: { containers: false } },
+          placement: "containerOnly",
+        },
+        orphan: {
+          children: { allow: { containers: false } },
+          placement: "containerOnly",
+        },
+      }),
+    ).toThrow(/could never be inserted/);
+  });
+
+  // A container may have its own content: it becomes a node holding a content
+  // node and a children node.
+  it("accepts `children` on a block with inline content", () => {
+    expect(() =>
+      validateChildrenConfigs({
+        toggle: { type: "toggle", content: "inline", children: { min: 1 } },
+      }),
+    ).not.toThrow();
+  });
+
+  it("rejects `children` on a table block", () => {
+    expect(() =>
+      validateChildrenConfigs({
+        bad: { type: "bad", content: "table", children: { min: 1 } },
+      }),
+    ).toThrow(/cannot be combined with `content: "table"`/);
+  });
+
+  // The content & children nodes are generated from the block type, so a block
+  // type that happens to have one of those names would clash with them.
+  it("rejects a block type that collides with a generated node name", () => {
+    expect(() =>
+      validateChildrenConfigs({
+        toggle: { type: "toggle", content: "inline", children: {} },
+        toggle__content: { type: "toggle__content", content: "inline" },
+      }),
+    ).toThrow(/collides with the block type of the same name/);
+  });
+
+  // `fillBefore` recurses across node types, so a cycle blows the stack rather
+  // than returning null — it has to be caught before the schema is built.
+  it("rejects a container cycle", () => {
+    expect(
+      validate({
+        card: {
+          children: { allow: { blocks: false, containers: ["cardBody"] } },
+        },
+        cardBody: {
+          children: { allow: { blocks: false, containers: ["card"] } },
+          placement: "containerOnly",
+        },
+      }),
+    ).toThrow(/requires it back/);
+  });
+
+  it("accepts a mutual reference when one side allows regular blocks", () => {
+    // A slot that accepts regular blocks can always be filled with a
+    // paragraph, so it breaks the cycle.
+    expect(
+      validate({
+        card: {
+          children: { allow: { blocks: false, containers: ["cardBody"] } },
+        },
+        cardBody: {
+          children: { allow: { blocks: true, containers: ["card"] } },
+          placement: "containerOnly",
+        },
+      }),
+    ).not.toThrow();
+  });
+});
diff --git a/packages/core/src/schema/blocks/validateChildren.ts b/packages/core/src/schema/blocks/validateChildren.ts
new file mode 100644
index 0000000000..ea7f8df8eb
--- /dev/null
+++ b/packages/core/src/schema/blocks/validateChildren.ts
@@ -0,0 +1,392 @@
+import {
+  containerChildrenNodeName,
+  containerContentNodeName,
+  getChildrenConfig,
+  isContainerType,
+  isPlaceableAnywhere,
+  resolveChildren,
+} from "./children.js";
+import type {
+  BlockConfig,
+  ChildrenConfig,
+  ResolvedChildren,
+  ResolvedSlot,
+} from "./types.js";
+
+type ValidatableConfig = Pick<BlockConfig, "type" | "content"> & {
+  children?: ChildrenConfig;
+  placement?: BlockConfig["placement"];
+};
+
+/**
+ * Validates the `children` config of every block in a schema, so that
+ * misconfigurations surface as a clear error at schema-creation time instead
+ * of as an opaque ProseMirror one (or a stack overflow) much later.
+ *
+ * @param blockConfigs The configs of every block in the schema, keyed by type.
+ */
+export function validateChildrenConfigs(
+  blockConfigs: Record<string, ValidatableConfig>,
+) {
+  const isContainerBlockType = (blockType: string) =>
+    !!blockConfigs[blockType] && isContainerType(blockConfigs[blockType]);
+
+  for (const [type, config] of Object.entries(blockConfigs)) {
+    const children = getChildrenConfig(config);
+
+    if (!children) {
+      if (config.placement !== undefined) {
+        fail(
+          type,
+          "`placement` only applies to container blocks, but this block does not declare `children`. Regular blocks can always be placed anywhere.",
+        );
+      }
+      continue;
+    }
+
+    validateOne(type, config, children, blockConfigs, isContainerBlockType);
+  }
+
+  validateContainerOnlyIsReachable(blockConfigs);
+  validateNoCycles(blockConfigs, isContainerBlockType);
+}
+
+function fail(type: string, message: string): never {
+  throw new Error(
+    `Invalid \`children\` config for block "${type}": ${message}`,
+  );
+}
+
+function validateOne(
+  type: string,
+  config: ValidatableConfig,
+  children: ChildrenConfig,
+  blockConfigs: Record<string, unknown>,
+  isContainerBlockType: (blockType: string) => boolean,
+) {
+  // A container may have its own content: it then becomes a node holding a
+  // content node and a children node. A table can't — its content is already
+  // a node tree of its own, with nowhere to put the children node.
+  if (config.content === "table") {
+    fail(
+      type,
+      '`children` cannot be combined with `content: "table"`. A table block\'s content is already a structure of its own.',
+    );
+  }
+
+  if (config.content !== "none") {
+    // The content & children nodes are generated from the block type, so a
+    // block type that happens to have the generated name would silently
+    // overwrite one of them.
+    for (const generated of [
+      containerContentNodeName(type),
+      containerChildrenNodeName(type),
+    ]) {
+      if (generated in blockConfigs) {
+        fail(
+          type,
+          `it has its own content as well as \`children\`, so it generates a node named "${generated}" — which collides with the block type of the same name. Rename one of the two.`,
+        );
+      }
+    }
+  }
+
+  if (children.sequence && children.sequence.length === 0) {
+    fail(type, "`sequence` must not be empty. Omit it for a uniform body.");
+  }
+
+  const resolved = resolveChildren(children);
+
+  resolved.slots.forEach((slot, index) => {
+    const where =
+      resolved.slots.length === 1 ? "" : ` (in \`sequence\` slot ${index})`;
+
+    if (!Number.isInteger(slot.min) || slot.min < 0) {
+      fail(
+        type,
+        `minimum child count must be a non-negative integer, but is ${slot.min}${where}.`,
+      );
+    }
+    if (slot.max !== undefined) {
+      if (!Number.isInteger(slot.max) || slot.max < 1) {
+        fail(
+          type,
+          `maximum child count must be a positive integer, but is ${slot.max}${where}.`,
+        );
+      }
+      if (slot.max < slot.min) {
+        fail(
+          type,
+          `maximum child count (${slot.max}) must be greater than or equal to the minimum (${slot.min})${where}.`,
+        );
+      }
+    }
+
+    validateAllow(type, slot, where, blockConfigs, isContainerBlockType);
+  });
+
+  validateDefault(type, resolved, blockConfigs, isContainerBlockType);
+}
+
+function validateAllow(
+  type: string,
+  slot: ResolvedSlot,
+  where: string,
+  blockConfigs: Record<string, unknown>,
+  isContainerBlockType: (blockType: string) => boolean,
+) {
+  if (slot.containers !== true) {
+    for (const allowed of slot.containers) {
+      if (!(allowed in blockConfigs)) {
+        fail(
+          type,
+          `\`allow.containers\` contains "${allowed}", which is not a block type in this schema${where}.`,
+        );
+      }
+      // The whole point of splitting `allow` into `blocks` and `containers` is
+      // that each field maps onto something the schema can actually enforce.
+      // Silently accepting a regular block type here would put us right back
+      // to promising a restriction we cannot keep.
+      if (!isContainerBlockType(allowed)) {
+        fail(
+          type,
+          `\`allow.containers\` contains "${allowed}", which is a regular block, not a container block${where}. ` +
+            "BlockNote cannot restrict which regular block types a container accepts — every regular block is the same ProseMirror node. " +
+            "Use `allow: { blocks: true }` to accept regular blocks, or `allow: { blocks: false }` to reject them all.",
+        );
+      }
+    }
+  }
+
+  if (
+    !slot.blocks &&
+    slot.containers !== true &&
+    slot.containers.length === 0
+  ) {
+    fail(
+      type,
+      `\`allow\` permits nothing${where}. A container must accept at least one block or container type; drop \`children\` entirely for a block that holds none.`,
+    );
+  }
+
+  if (!slot.blocks && slot.containers === true) {
+    const hasContainer = Object.entries(blockConfigs).some(
+      ([blockType]) => isContainerBlockType(blockType) && blockType !== type,
+    );
+    if (!hasContainer) {
+      fail(
+        type,
+        `\`allow\` permits only container blocks${where}, but this schema has no other container block types.`,
+      );
+    }
+  }
+}
+
+function validateDefault(
+  type: string,
+  resolved: ResolvedChildren,
+  blockConfigs: Record<string, unknown>,
+  isContainerBlockType: (blockType: string) => boolean,
+) {
+  const { default: defaultChildren, minCount, maxCount } = resolved;
+  if (!defaultChildren) {
+    return;
+  }
+
+  if (defaultChildren.length < minCount) {
+    fail(
+      type,
+      `\`default\` has ${defaultChildren.length} block(s), fewer than the ${minCount} required.`,
+    );
+  }
+  if (maxCount !== undefined && defaultChildren.length > maxCount) {
+    fail(
+      type,
+      `\`default\` has ${defaultChildren.length} block(s), more than the ${maxCount} allowed.`,
+    );
+  }
+
+  // Walk the slots greedily so a `sequence` reports which position rejected
+  // the child rather than just "not permitted".
+  let slotIndex = 0;
+  let filled = 0;
+  for (const child of defaultChildren) {
+    const childType = child.type ?? "paragraph";
+    if (!(childType in blockConfigs)) {
+      fail(
+        type,
+        `\`default\` contains a block of type "${childType}", which is not a block type in this schema.`,
+      );
+    }
+
+    // Advance past any slot this child can't land in: one already at its `max`,
+    // or one that doesn't accept this type but has already met its `min` (so
+    // skipping it still leaves a valid fill). A slot still below its `min`
+    // can't be skipped — doing so would leave the default short on that slot.
+    while (slotIndex < resolved.slots.length) {
+      const candidate = resolved.slots[slotIndex];
+      const isFull = filled >= (candidate.max ?? Infinity);
+      const skippableMismatch =
+        filled >= candidate.min &&
+        !slotAccepts(candidate, childType, isContainerBlockType);
+      if (!isFull && !skippableMismatch) {
+        break;
+      }
+      slotIndex++;
+      filled = 0;
+    }
+    const slot = resolved.slots[slotIndex];
+    if (!slot) {
+      fail(type, `\`default\` has more blocks than \`sequence\` has room for.`);
+    }
+
+    if (!slotAccepts(slot, childType, isContainerBlockType)) {
+      const where =
+        resolved.slots.length === 1 ? "" : ` in \`sequence\` slot ${slotIndex}`;
+      fail(
+        type,
+        `\`default\` contains a block of type "${childType}", which is not permitted${where}.`,
+      );
+    }
+    filled++;
+  }
+}
+
+/**
+ * Whether a slot accepts a block type. Honest by construction: the schema's
+ * only lever for regular blocks is "is `blockContainer` in the union or not",
+ * so that is exactly what this asks.
+ */
+export function slotAccepts(
+  slot: ResolvedSlot,
+  blockType: string,
+  isContainerBlockType: (blockType: string) => boolean,
+): boolean {
+  if (isContainerBlockType(blockType)) {
+    return slot.containers === true || slot.containers.includes(blockType);
+  }
+  return slot.blocks;
+}
+
+/**
+ * Container nodes register in a priority band strictly below `blockContainer`
+ * (see `containerNodePriority`), which is below every regular block. So a
+ * container's `runsBefore` can only order it against other containers — naming
+ * a regular block there promises an ordering the schema cannot produce.
+ *
+ * @param blockConfigs The configs of every block in the schema, keyed by type.
+ * @param runsBefore The `runsBefore` each block's implementation declares.
+ */
+export function validateContainerRunsBefore(
+  blockConfigs: Record<string, ValidatableConfig>,
+  runsBefore: Record<string, readonly string[] | undefined>,
+) {
+  for (const [type, config] of Object.entries(blockConfigs)) {
+    if (!isContainerType(config)) {
+      continue;
+    }
+
+    for (const other of runsBefore[type] ?? []) {
+      // "default" is `sortByDependencies`' reference point rather than a block
+      // type, and a type that isn't in the schema is somebody else's error.
+      if (other === "default" || !(other in blockConfigs)) {
+        continue;
+      }
+      if (!isContainerType(blockConfigs[other])) {
+        throw new Error(
+          `Invalid \`runsBefore\` for container block "${type}": it names "${other}", which is a regular block, not a container block. ` +
+            "Container block nodes always register below regular ones, so a container can never be ordered before a regular block. " +
+            "`runsBefore` on a container can only name other container blocks.",
+        );
+      }
+    }
+  }
+}
+
+/**
+ * A `placement: "containerOnly"` block that no container accepts could never
+ * be inserted anywhere, which is always a mistake rather than a choice.
+ *
+ * Deliberately conservative: one container allowing *any* container type is
+ * taken as accepting all of them. Proving the stricter thing (that the block
+ * is reachable from a block placeable at the root) is full graph reachability,
+ * and this check exists to catch typos, not to police schema topology.
+ */
+function validateContainerOnlyIsReachable(
+  blockConfigs: Record<string, ValidatableConfig>,
+) {
+  const accepted = new Set<string>();
+  for (const config of Object.values(blockConfigs)) {
+    const children = getChildrenConfig(config);
+    if (!children) {
+      continue;
+    }
+    for (const slot of resolveChildren(children).slots) {
+      if (slot.containers === true) {
+        return; // some container accepts every container type
+      }
+      for (const allowed of slot.containers) {
+        accepted.add(allowed);
+      }
+    }
+  }
+
+  for (const [type, config] of Object.entries(blockConfigs)) {
+    if (!isPlaceableAnywhere(config) && !accepted.has(type)) {
+      fail(
+        type,
+        `it declares \`placement: "containerOnly"\`, but no container's \`children.allow.containers\` includes it, so it could never be inserted.`,
+      );
+    }
+  }
+}
+
+/**
+ * A container that requires a child which in turn requires it back can never
+ * be created: ProseMirror's `fillBefore` recurses across node types and blows
+ * the stack rather than returning `null`. So this has to be caught statically,
+ * before the schema is built.
+ */
+function validateNoCycles(
+  blockConfigs: Record<string, ValidatableConfig>,
+  isContainerBlockType: (blockType: string) => boolean,
+) {
+  // A slot that allows regular blocks can always be filled with a plain
+  // paragraph, so it never forces recursion — only container-only slots do.
+  const requiredContainers = (type: string): string[] => {
+    const children = getChildrenConfig(blockConfigs[type]);
+    if (!children) {
+      return [];
+    }
+    return resolveChildren(children).slots.flatMap((slot) =>
+      slot.min >= 1 && !slot.blocks && slot.containers !== true
+        ? slot.containers.filter(isContainerBlockType)
+        : [],
+    );
+  };
+
+  const state = new Map<string, "visiting" | "done">();
+
+  const visit = (type: string, path: string[]) => {
+    const seen = state.get(type);
+    if (seen === "done") {
+      return;
+    }
+    if (seen === "visiting") {
+      fail(
+        type,
+        `it requires a child that requires it back (${[...path, type].join(" -> ")}), so it could never be created. Allow regular blocks in one of the slots to break the cycle.`,
+      );
+    }
+
+    state.set(type, "visiting");
+    for (const next of requiredContainers(type)) {
+      visit(next, [...path, type]);
+    }
+    state.set(type, "done");
+  };
+
+  for (const type of Object.keys(blockConfigs)) {
+    visit(type, []);
+  }
+}
diff --git a/packages/core/src/schema/index.ts b/packages/core/src/schema/index.ts
index 2f1e703007..674a0bdb96 100644
--- a/packages/core/src/schema/index.ts
+++ b/packages/core/src/schema/index.ts
@@ -1,3 +1,10 @@
+// `children.js` and `validateChildren.js` are deliberately *not* re-exported
+// wholesale: almost everything in them is machinery for compiling a `children`
+// config into a ProseMirror content expression, which lives on
+// `@blocknote/core/internal` (see `src/internal.ts`). Only the question a block
+// author asks — "is this a container?" — belongs here; the config types come
+// from `./blocks/types.js` below.
+export { isContainerType } from "./blocks/children.js";
 export * from "./blocks/createSpec.js";
 export * from "./blocks/internal.js";
 export * from "./blocks/types.js";
diff --git a/packages/core/src/schema/schema.ts b/packages/core/src/schema/schema.ts
index a7a04e93dc..eba0017f75 100644
--- a/packages/core/src/schema/schema.ts
+++ b/packages/core/src/schema/schema.ts
@@ -16,6 +16,12 @@ import {
   getInlineContentSchemaFromSpecs,
   getStyleSchemaFromSpecs,
 } from "./index.js";
+import { isContainerType } from "./blocks/children.js";
+import type { BlockSchemaContext } from "./blocks/createSpec.js";
+import {
+  validateChildrenConfigs,
+  validateContainerRunsBefore,
+} from "./blocks/validateChildren.js";
 
 function removeUndefined<T extends Record<string, any> | undefined>(obj: T): T {
   if (!obj) {
@@ -91,6 +97,38 @@ export class CustomBlockNoteSchema<
       })),
     );
 
+    // Container-ness is needed to build *other* blocks' nodes (a container's
+    // `allow.containers` maps block types to node terms, and only container
+    // types are their own node type), so it's resolved across the whole schema
+    // up front. Validation runs first so misconfigurations surface as clear
+    // errors rather than as opaque ProseMirror ones.
+    const blockConfigs = Object.fromEntries(
+      Object.entries(this.opts.blockSpecs).map(([key, blockSpec]) => [
+        key,
+        blockSpec.config,
+      ]),
+    );
+
+    validateChildrenConfigs(blockConfigs);
+    validateContainerRunsBefore(
+      blockConfigs,
+      Object.fromEntries(
+        Object.entries(this.opts.blockSpecs).map(([key, blockSpec]) => [
+          key,
+          blockSpec.implementation?.runsBefore,
+        ]),
+      ),
+    );
+
+    const isContainerBlockType = (blockType: string) =>
+      !!blockConfigs[blockType] && isContainerType(blockConfigs[blockType]);
+
+    const schemaContext: BlockSchemaContext = {
+      isContainerBlockType,
+      containerBlockTypes: () =>
+        Object.keys(blockConfigs).filter(isContainerBlockType),
+    };
+
     const blockSpecs = Object.fromEntries(
       Object.entries(this.opts.blockSpecs).map(([key, blockSpec]) => {
         return [
@@ -100,6 +138,7 @@ export class CustomBlockNoteSchema<
             blockSpec.implementation,
             blockSpec.extensions,
             getPriority(key),
+            schemaContext,
           ),
         ];
       }),
diff --git a/packages/core/src/y/extensions/AttributionExtension.test.ts b/packages/core/src/y/extensions/AttributionExtension.test.ts
index df0267f093..f752b48182 100644
--- a/packages/core/src/y/extensions/AttributionExtension.test.ts
+++ b/packages/core/src/y/extensions/AttributionExtension.test.ts
@@ -17,15 +17,14 @@ const editors: BlockNoteEditor[] = [];
 // No Yjs/collaboration needed — the extension's load plugin only cares that a
 // transaction adds a `y-attributed-*` mark, which we do directly below.
 function createEditor() {
-  const resolveUsers = vi.fn(
-    async (ids: string[]): Promise<User[]> =>
-      ids.map((id) => ({
-        id,
-        username: `name-${id}`,
-        avatarUrl: "",
-        color: "#123456",
-        colorLight: "#abcdef",
-      })),
+  const resolveUsers = vi.fn(async (ids: string[]): Promise<User[]> =>
+    ids.map((id) => ({
+      id,
+      username: `name-${id}`,
+      avatarUrl: "",
+      color: "#123456",
+      colorLight: "#abcdef",
+    })),
   );
 
   const editor = BlockNoteEditor.create({
diff --git a/packages/core/src/yjs/extensions/FixUpSchema.ts b/packages/core/src/yjs/extensions/FixUpSchema.ts
index 37fb1fd4e9..7dc3f4253d 100644
--- a/packages/core/src/yjs/extensions/FixUpSchema.ts
+++ b/packages/core/src/yjs/extensions/FixUpSchema.ts
@@ -25,7 +25,15 @@ export const FixUpSchemaExtension = createExtension(({ editor }) => {
 
       // create a copy that we can mutate (otherwise, assigning attrs is not safe and corrupts the pm state)
       const jsonNode = JSON.parse(JSON.stringify(ret.toJSON()));
-      jsonNode.content[0].content[0].attrs.id = "initialBlockId";
+      // The first fill of the doc's blockGroup is guaranteed to be a
+      // `blockContainer` (container block nodes register at lower priority
+      // precisely so auto-fill picks `blockContainer` first), but guard on
+      // the node actually carrying an id attr in case a custom schema
+      // changes that.
+      const firstBlock = jsonNode.content?.[0]?.content?.[0];
+      if (firstBlock?.attrs && "id" in firstBlock.attrs) {
+        firstBlock.attrs.id = "initialBlockId";
+      }
 
       cache = Node.fromJSON(schema, jsonNode);
       return cache;
diff --git a/packages/core/vite.config.ts b/packages/core/vite.config.ts
index 2763b9723c..4f743d69fe 100644
--- a/packages/core/vite.config.ts
+++ b/packages/core/vite.config.ts
@@ -35,6 +35,7 @@ export default defineConfig({
         blocks: path.resolve(__dirname, "src/blocks/index.ts"),
         locales: path.resolve(__dirname, "src/i18n/index.ts"),
         extensions: path.resolve(__dirname, "src/extensions/index.ts"),
+        internal: path.resolve(__dirname, "src/internal.ts"),
         yjs: path.resolve(__dirname, "src/yjs/index.ts"),
         y: path.resolve(__dirname, "src/y/index.ts"),
       },
diff --git a/packages/core/vitestSetup.ts b/packages/core/vitestSetup.ts
index bf9678c8f8..23642824a6 100644
--- a/packages/core/vitestSetup.ts
+++ b/packages/core/vitestSetup.ts
@@ -1,11 +1,18 @@
 import { afterEach, beforeEach } from "vite-plus/test";
 
+// This setup file also runs for test files that opt into the plain `node`
+// environment (`@vitest-environment node`), where there is no `window` at all.
+// `__TEST_OPTIONS` (which drives deterministic block IDs) therefore hangs off
+// `window` when there is one and off `globalThis` otherwise — the same
+// resolution `UniqueID`'s `generateID` uses.
+const testHost: any = (globalThis as any).window ?? globalThis;
+
 beforeEach(() => {
-  (window as Window & { __TEST_OPTIONS?: any }).__TEST_OPTIONS = {};
+  testHost.__TEST_OPTIONS = {};
 });
 
 afterEach(() => {
-  delete (window as Window & { __TEST_OPTIONS?: any }).__TEST_OPTIONS;
+  delete testHost.__TEST_OPTIONS;
 });
 
 // Mock ClipboardEvent
diff --git a/packages/react/src/components/Popovers/BlockPopover.tsx b/packages/react/src/components/Popovers/BlockPopover.tsx
index 2bf0e4fa57..57f340afb2 100644
--- a/packages/react/src/components/Popovers/BlockPopover.tsx
+++ b/packages/react/src/components/Popovers/BlockPopover.tsx
@@ -1,4 +1,4 @@
-import { getNodeById } from "@blocknote/core";
+import { getNodeById, isContainerNode } from "@blocknote/core";
 import { ReactNode, useMemo } from "react";
 
 import { useBlockNoteEditor } from "../../hooks/useBlockNoteEditor.js";
@@ -29,6 +29,28 @@ export const BlockPopover = (
           return undefined;
         }
 
+        // For container blocks the PM node IS the block, so a position
+        // inside it resolves to its contentDOM — the child-blocks area —
+        // which would anchor the popover to the first child's rows instead
+        // of the block's own element.
+        if (isContainerNode(nodePosInfo.node.type)) {
+          const dom = editor.prosemirrorView.nodeDOM(nodePosInfo.posBeforeNode);
+          // Frameworks like React wrap the node view in a `display: contents`
+          // element that has no box of its own (a zero-size bounding rect), so
+          // anchoring to it would place the popover at (0, 0). The block's
+          // actual box is the author's root element inside it, which core
+          // stamps with `data-node-type`; vanilla containers render that boxed
+          // element directly as the node view's DOM.
+          if (dom instanceof Element) {
+            const boxed = dom.matches("[data-node-type]")
+              ? dom
+              : dom.querySelector("[data-node-type]");
+            if (boxed) {
+              return { element: boxed };
+            }
+          }
+        }
+
         const { node } = editor.prosemirrorView.domAtPos(
           nodePosInfo.posBeforeNode + 1,
         );
diff --git a/packages/react/src/editor/styles.css b/packages/react/src/editor/styles.css
index 507f2cd46f..c3a39005a5 100644
--- a/packages/react/src/editor/styles.css
+++ b/packages/react/src/editor/styles.css
@@ -111,6 +111,13 @@
   width: 100%;
 }
 
+/* Container blocks own their outer DOM: the block's root element is the one
+   its `render` returned, so the wrapper React needs around it must not be a
+   box of its own. */
+.bn-react-node-view-renderer.bn-container-node-view {
+  display: contents;
+}
+
 /* Indent line styling */
 .bn-block-group
   .bn-block:not(:has(.bn-toggle-wrapper))
diff --git a/packages/react/src/schema/ReactBlockSpec.container.browser.test.tsx b/packages/react/src/schema/ReactBlockSpec.container.browser.test.tsx
new file mode 100644
index 0000000000..3d8e736e48
--- /dev/null
+++ b/packages/react/src/schema/ReactBlockSpec.container.browser.test.tsx
@@ -0,0 +1,168 @@
+import { BlockNoteEditor, BlockNoteSchema } from "@blocknote/core";
+import { flushSync } from "react-dom";
+import { createRoot, type Root } from "react-dom/client";
+import { afterEach, describe, expect, it } from "vite-plus/test";
+
+import { BlockNoteViewRaw } from "../editor/BlockNoteView.js";
+import { createReactBlockSpec } from "./ReactBlockSpec.js";
+
+/**
+ * The DOM output of React container blocks, in a real browser.
+ *
+ * Both halves need a DOM that actually exists: the external-HTML path renders
+ * the block through a temporary `createRoot` (see `@util/ReactRenderUtil`), and
+ * a React node view only runs at all once `contentComponent` is set, which
+ * happens when `BlockNoteViewRaw` mounts the editor. Runs in the tests
+ * package's browser suite; the document-level assertions live next door in
+ * `ReactBlockSpec.container.test.tsx` (node).
+ *
+ * Layout facts (`display: contents` hosts, box geometry) and the content +
+ * children region ordering are covered by
+ * `tests/src/end-to-end/containerblocks/containerblocks.test.tsx`.
+ */
+
+// A pure container: its `contentRef` element holds its child blocks.
+const createCallout = createReactBlockSpec(
+  {
+    type: "callout",
+    propSchema: { flavor: { default: "tip" } },
+    content: "none",
+    children: { min: 1, default: [{ type: "paragraph" }] },
+  },
+  {
+    render: (props) => (
+      <div className="callout">
+        <div className="callout-body" ref={props.contentRef} />
+      </div>
+    ),
+  },
+);
+
+const schema = BlockNoteSchema.create().extend({
+  blockSpecs: { callout: createCallout() },
+});
+
+describe("React container block external HTML", () => {
+  it("does not wrap containers in a blockContent div", () => {
+    // Headless: the React `toExternalHTML` path renders through a temporary
+    // React root, which is why this still needs a real document.
+    const editor = BlockNoteEditor.create({ schema });
+
+    const html = editor.blocksToHTMLLossy([
+      {
+        type: "callout",
+        id: "c-0",
+        children: [{ id: "c-p-0", type: "paragraph", content: "Hello" }],
+      },
+    ] as any);
+
+    // Container blocks own their outer DOM entirely — regression test for the
+    // React `toExternalHTML` path wrapping them in a spurious
+    // `bn-block-content` div (core's `createBlockSpec` passes them through).
+    expect(html).not.toContain('data-content-type="callout"');
+    expect(html).toContain('data-node-type="callout"');
+    expect(html).toContain("Hello");
+  });
+
+  it("puts container attributes on the block's own root element", () => {
+    // The serialized root is the element the block's `render` returned — no
+    // wrapper of React's in between — so `.callout[data-flavor]` CSS matches
+    // the same element here as it does in the live editor (below).
+    const editor = BlockNoteEditor.create({ schema });
+
+    const html = editor.blocksToHTMLLossy([
+      { type: "callout", id: "c-0", children: [{ type: "paragraph" }] },
+    ] as any);
+
+    expect(html).toContain('class="callout"');
+    expect(html).toContain('data-node-type="callout"');
+    expect(html).not.toContain("data-node-view-wrapper");
+  });
+});
+
+let root: Root | undefined;
+let div: HTMLDivElement | undefined;
+let editor: BlockNoteEditor<any, any, any> | undefined;
+
+afterEach(() => {
+  root?.unmount();
+  root = undefined;
+  if (div) {
+    document.body.removeChild(div);
+    div = undefined;
+  }
+  editor?._tiptapEditor.destroy();
+  editor = undefined;
+});
+
+/** Lets TipTap's deferred node-view render and React's commit run. */
+const tick = () => new Promise((resolve) => setTimeout(resolve, 0));
+
+async function mountEditor(initialContent: any[]) {
+  div = document.createElement("div");
+  document.body.appendChild(div);
+
+  editor = BlockNoteEditor.create({
+    schema,
+    trailingBlock: false,
+    initialContent,
+  }) as BlockNoteEditor<any, any, any>;
+
+  root = createRoot(div);
+  flushSync(() => {
+    root!.render(<BlockNoteViewRaw editor={editor as any} />);
+  });
+  // TipTap only renders a node view synchronously when this is set; BlockNote
+  // mounts the editor itself and never does, so the first batch of node views
+  // takes the deferred path (see `tests/src/unit/react/staleNodeViewPos.test.tsx`).
+  (editor as any)._tiptapEditor.isEditorContentInitialized = true;
+  await tick();
+
+  return { editor: editor!, div: div! };
+}
+
+describe("React container block node view", () => {
+  it("stamps only non-default props onto the block's own root, and keeps them in sync", async () => {
+    const mounted = await mountEditor([
+      { id: "c-0", type: "callout", children: [{ type: "paragraph" }] },
+    ]);
+
+    const calloutRoot = mounted.div.querySelector<HTMLElement>(".callout")!;
+    // The author's element, not `div.react-renderer` or the node view wrapper —
+    // exactly the class the author wrote, and nothing else.
+    expect(calloutRoot.className).toBe("callout");
+    expect(calloutRoot.getAttribute("data-id")).toBe("c-0");
+    // `flavor` is at its default, so no attribute is written for it.
+    expect(calloutRoot.hasAttribute("data-flavor")).toBe(false);
+
+    mounted.editor.updateBlock("c-0", { props: { flavor: "warning" } } as any);
+    await tick();
+
+    // Re-queried: a prop change must land on whatever element is now the
+    // block's root, so `.callout[data-flavor="warning"]` selects in the live
+    // editor exactly as it does in the serialized HTML above.
+    expect(
+      mounted.div
+        .querySelector<HTMLElement>(".callout")!
+        .getAttribute("data-flavor"),
+    ).toBe("warning");
+  });
+
+  it("mounts a pure container's children inside its `contentRef` element", async () => {
+    const mounted = await mountEditor([
+      {
+        id: "c-0",
+        type: "callout",
+        children: [{ id: "c-child", type: "paragraph", content: "Child" }],
+      },
+    ]);
+
+    const body = mounted.div.querySelector<HTMLElement>(".callout-body")!;
+    // A container with no content of its own puts its children where the
+    // author placed `contentRef` — not somewhere else in the node view. The
+    // child's own block element is a descendant, so this is structure, not
+    // just text that happened to bubble up.
+    expect(body.querySelector('[data-id="c-child"]')).not.toBeNull();
+    expect(body.textContent).toBe("Child");
+  });
+});
diff --git a/packages/react/src/schema/ReactBlockSpec.container.test.tsx b/packages/react/src/schema/ReactBlockSpec.container.test.tsx
new file mode 100644
index 0000000000..9a1af7d644
--- /dev/null
+++ b/packages/react/src/schema/ReactBlockSpec.container.test.tsx
@@ -0,0 +1,179 @@
+/**
+ * @vitest-environment node
+ *
+ * Document-level tests for React container blocks. Every assertion here reads
+ * `editor.document`, so there is nothing to render and no DOM to need — the
+ * node environment keeps that honest. The DOM output (serialized HTML and the
+ * live node view) is covered by `ReactBlockSpec.container.browser.test.tsx`.
+ */
+import {
+  BlockNoteEditor,
+  BlockNoteSchema,
+  defaultBlockSpecs,
+} from "@blocknote/core";
+import { beforeEach, describe, expect, it } from "vite-plus/test";
+
+import { createReactBlockSpec } from "./ReactBlockSpec.js";
+
+// Same shape as the example callout block (`examples/06-custom-schema/09-container-block`).
+const Callout = createReactBlockSpec(
+  {
+    type: "callout" as const,
+    propSchema: {},
+    content: "none" as const,
+    children: { min: 1, default: [{ type: "paragraph" }] },
+  },
+  {
+    render: ({ contentRef }) => (
+      <div className="callout">
+        <div className="callout-body" ref={contentRef} />
+      </div>
+    ),
+  },
+)();
+
+// The additivity claim: adding `children` to an existing block is one config
+// line and *zero* render changes. Both blocks below share this render, which is
+// the shape every inline-content React block already has — `contentRef` on a
+// plain div. `Alert` is `examples/06-custom-schema/01-alert-block` reduced to
+// its structure; `AlertWithBody` is the same block with `children` added.
+const renderAlert = ({ contentRef }: { contentRef: (el: any) => void }) => (
+  <div className="alert">
+    <div className="alert-icon-wrapper" contentEditable={false} />
+    <div className="inline-content" ref={contentRef} />
+  </div>
+);
+
+const Alert = createReactBlockSpec(
+  {
+    type: "alert" as const,
+    propSchema: { flavor: { default: "warning" } },
+    content: "inline" as const,
+  },
+  { render: renderAlert },
+)();
+
+const AlertWithBody = createReactBlockSpec(
+  {
+    type: "alertWithBody" as const,
+    propSchema: { flavor: { default: "warning" } },
+    content: "inline" as const,
+    children: { min: 1 },
+  },
+  { render: renderAlert },
+)();
+
+const schema = BlockNoteSchema.create().extend({
+  blockSpecs: {
+    ...defaultBlockSpecs,
+    callout: Callout,
+    alert: Alert,
+    alertWithBody: AlertWithBody,
+  } as const,
+});
+
+const defaultParagraphProps = {
+  backgroundColor: "default",
+  textAlignment: "left",
+  textColor: "default",
+};
+
+/**
+ * The document without block ids. Converting a block generates fresh ids, and
+ * core's deterministic test-id hook (`UniqueID`'s `generateID`) only kicks in
+ * when a `window` exists — under node it falls back to real UUIDs. Ids that
+ * matter are asserted individually.
+ */
+const withoutIds = (blocks: any[]): any[] =>
+  blocks.map(({ id: _id, children, ...rest }) => ({
+    ...rest,
+    children: withoutIds(children),
+  }));
+
+describe("React updateBlock → container with `default` (document-level)", () => {
+  const editor = BlockNoteEditor.create({ schema });
+
+  beforeEach(() => {
+    editor.replaceBlocks(editor.document, [
+      { id: "p-0", type: "paragraph", content: "" },
+      { id: "trailing", type: "paragraph", content: "" },
+    ]);
+  });
+
+  it("converts an empty paragraph to a callout via editor.updateBlock", () => {
+    editor.updateBlock("p-0", { type: "callout" });
+
+    expect(withoutIds(editor.document)).toEqual([
+      {
+        type: "callout",
+        props: {},
+        // `content: "none"`, so the block has no inline content of its own —
+        // and the `children.default` seeded it exactly one empty paragraph.
+        content: undefined,
+        children: [
+          {
+            type: "paragraph",
+            props: defaultParagraphProps,
+            content: [],
+            children: [],
+          },
+        ],
+      },
+      {
+        type: "paragraph",
+        props: defaultParagraphProps,
+        content: [],
+        children: [],
+      },
+    ]);
+    // The block that wasn't converted keeps its identity.
+    expect(editor.document[1].id).toBe("trailing");
+  }, 5000);
+});
+
+// The plan's headline claim: `children` is additive. Adding it to a block gives
+// that block a body without touching its `render` — the block's `contentRef`
+// element goes from holding just its inline content to holding its inline
+// content followed by its child blocks.
+describe("adding `children` to an existing block", () => {
+  const editor = BlockNoteEditor.create({ schema });
+
+  it("keeps the block without `children` unchanged", () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "a-0", type: "alert", content: "Heads up" },
+    ] as any);
+
+    const block = editor.getBlock("a-0")!;
+    expect(block.content).toEqual([
+      { type: "text", text: "Heads up", styles: {} },
+    ]);
+    expect(block.children).toEqual([]);
+  }, 5000);
+
+  it("gains a body that accepts child blocks, with the same render", () => {
+    editor.replaceBlocks(editor.document, [
+      {
+        id: "b-0",
+        type: "alertWithBody",
+        content: "Heads up",
+        children: [{ id: "b-child", type: "paragraph", content: "Details" }],
+      },
+    ] as any);
+
+    const block = editor.getBlock("b-0")!;
+    expect(block.content).toEqual([
+      { type: "text", text: "Heads up", styles: {} },
+    ]);
+    expect(block.children.map((child) => child.id)).toEqual(["b-child"]);
+    // The child is an ordinary block of the document, reachable by id.
+    expect(editor.getBlock("b-child")).toBeDefined();
+  }, 5000);
+
+  it("seeds a body when inserted without children", () => {
+    editor.replaceBlocks(editor.document, [
+      { id: "c-0", type: "alertWithBody", content: "Heads up" },
+    ] as any);
+
+    expect(editor.getBlock("c-0")!.children).toHaveLength(1);
+  }, 5000);
+});
diff --git a/packages/react/src/schema/ReactBlockSpec.tsx b/packages/react/src/schema/ReactBlockSpec.tsx
index 5311d4e37d..9dff8ac9dc 100644
--- a/packages/react/src/schema/ReactBlockSpec.tsx
+++ b/packages/react/src/schema/ReactBlockSpec.tsx
@@ -1,3 +1,4 @@
+import { applyContainerAttributes } from "@blocknote/core/internal";
 import {
   BlockConfig,
   BlockConfigOrCreator,
@@ -6,11 +7,14 @@ import {
   BlockNoteEditor,
   BlockSpec,
   camelToDataKebab,
+  ChildrenConfig,
   CustomBlockImplementation,
   Extension,
   ExtensionFactoryInstance,
   ExtractBlockConfigFromConfigOrCreator,
+  isContainerType,
   mergeCSSClasses,
+  nodeToBlock,
   Props,
   PropSchema,
 } from "@blocknote/core";
@@ -20,12 +24,29 @@ import {
   ReactNodeViewRenderer,
   useReactNodeView,
 } from "@tiptap/react";
-import { FC, ReactNode } from "react";
+import { CSSProperties, FC, ReactNode, useLayoutEffect } from "react";
 import { renderToDOMSpec } from "./@util/ReactRenderUtil.js";
 import { useNodeViewBlock } from "./useNodeViewBlock.js";
 
 // this file is mostly analogoues to `customBlocks.ts`, but for React blocks
 
+// A container block's root element is the block's own element, so every
+// wrapper React puts above it has to contribute no box of its own. Module
+// scope so the style object is referentially stable across renders.
+const DISPLAY_CONTENTS: CSSProperties = { display: "contents" };
+
+/**
+ * Whether the block has an editable region for its `render` to place: its
+ * inline content, its child blocks, or — for a container that also has its own
+ * content — both. Only a `content: "none"` block without `children` has
+ * nothing to place, and so is the only kind that doesn't get a `contentRef`.
+ */
+type HasEditableRegion<Config> = Config extends { children: ChildrenConfig }
+  ? true
+  : Config extends { content: "none" }
+    ? false
+    : true;
+
 export type ReactCustomBlockRenderProps<
   B extends BlockConfigOrCreator,
   Config extends ExtractBlockConfigFromConfigOrCreator<B> =
@@ -33,11 +54,16 @@ export type ReactCustomBlockRenderProps<
 > = {
   block: BlockNoDefaults<Record<Config["type"], Config>, any, any>;
   editor: BlockNoteEditor<Record<Config["type"], Config>, any, any>;
-} & (Config["content"] extends "inline" | "plain"
-  ? {
-      contentRef: (node: HTMLElement | null) => void;
-    }
-  : object);
+} & (Config["content"] extends "table"
+  ? object
+  : HasEditableRegion<Config> extends true
+    ? {
+        // Points to where the block's editable region mounts: its inline
+        // content, its child blocks, or — for a container that has its own
+        // content — its content followed by its children.
+        contentRef: (node: HTMLElement | null) => void;
+      }
+    : object);
 
 // extend BlockConfig but use a React render function
 export type ReactCustomBlockImplementation<
@@ -131,20 +157,20 @@ export function createReactBlockSpec<
   const TName extends string,
   const TProps extends PropSchema,
   const TContent extends "inline" | "none" | "plain",
+  // Inferred from the config object itself rather than widened to
+  // `BlockConfig<...>`, so `children` survives into the render props and
+  // `contentRef` is offered exactly when the block has an editable region.
+  const BlockConf extends BlockConfig<TName, TProps, TContent>,
   const TOptions extends Record<string, any> | undefined = undefined,
 >(
-  blockConfigOrCreator: BlockConfig<TName, TProps, TContent>,
+  blockConfigOrCreator: BlockConf,
   blockImplementationOrCreator:
-    | ReactCustomBlockImplementation<BlockConfig<TName, TProps, TContent>>
+    | ReactCustomBlockImplementation<BlockConf>
     | (TOptions extends undefined
-        ? () => ReactCustomBlockImplementation<
-            BlockConfig<TName, TProps, TContent>
-          >
+        ? () => ReactCustomBlockImplementation<BlockConf>
         : (
             options: Partial<TOptions>,
-          ) => ReactCustomBlockImplementation<
-            BlockConfig<TName, TProps, TContent>
-          >),
+          ) => ReactCustomBlockImplementation<BlockConf>),
   extensionsOrCreator?:
     | (ExtensionFactoryInstance | Extension)[]
     | (TOptions extends undefined
@@ -152,7 +178,13 @@ export function createReactBlockSpec<
         : (
             options: Partial<TOptions>,
           ) => (ExtensionFactoryInstance | Extension)[]),
-): (options?: Partial<TOptions>) => BlockSpec<TName, TProps, TContent>;
+): (
+  options?: Partial<TOptions>,
+) => BlockSpec<
+  BlockConf["type"],
+  BlockConf["propSchema"],
+  BlockConf["content"]
+>;
 export function createReactBlockSpec<
   const TName extends string,
   const TProps extends PropSchema,
@@ -230,10 +262,33 @@ export function createReactBlockSpec<
       implementation: {
         ...blockImplementation,
         toExternalHTML(block, editor, context) {
-          const BlockContent =
-            blockImplementation.toExternalHTML || blockImplementation.render;
+          const isContainer = isContainerType(blockConfig);
+          const BlockContent = (blockImplementation.toExternalHTML ||
+            blockImplementation.render) as FC<any>;
           const output = renderToDOMSpec((refCB) => {
-            return (
+            const content = (
+              <BlockContent
+                block={block as any}
+                editor={editor as any}
+                contentRef={(element: HTMLElement | null) => {
+                  refCB(element);
+                  if (element && !isContainer) {
+                    element.className = mergeCSSClasses(
+                      "bn-inline-content",
+                      element.className,
+                    );
+                  }
+                }}
+                context={context}
+              />
+            );
+            // A container block's render output *is* the block's root element.
+            // No wrapper of any kind, so the attributes core stamps
+            // afterwards land on the author's own element — the same element
+            // they land on in the live editor.
+            return isContainer ? (
+              content
+            ) : (
               <BlockContentWrapper
                 blockType={block.type}
                 blockProps={block.props}
@@ -243,20 +298,7 @@ export function createReactBlockSpec<
                   blockImplementation.meta?.fileBlockAccept !== undefined
                 }
               >
-                <BlockContent
-                  block={block as any}
-                  editor={editor as any}
-                  contentRef={(element) => {
-                    refCB(element);
-                    if (element) {
-                      element.className = mergeCSSClasses(
-                        "bn-inline-content",
-                        element.className,
-                      );
-                    }
-                  }}
-                  context={context}
-                />
+                {content}
               </BlockContentWrapper>
             );
           }, editor);
@@ -268,78 +310,200 @@ export function createReactBlockSpec<
             // constructed (itself guarded, via `getBlockFromNodeView`). Seeds
             // the fallback below so there is always something to render.
             const initialBlock = block;
+            // Container-ness is fixed per spec, so the node-view component
+            // can be chosen once — each variant is straight-line code using
+            // only the hooks and wrappers it needs.
+            const isContainer = isContainerType(blockConfig);
+            const BlockContent = blockImplementation.render as FC<any>;
+            const blockContentDOMAttributes = this.blockContentDOMAttributes;
+
+            // Set by the container node view's `NodeViewWrapper` below. The
+            // author's own root element is that wrapper's first element child;
+            // it's read lazily because React may not have committed yet when
+            // this node view is handed to core, and because the author's
+            // component is free to swap its root element on a re-render.
+            const wrapper: { current: HTMLElement | null } = { current: null };
+            const authorRootDOM = () =>
+              (wrapper.current?.firstElementChild as HTMLElement | null) ??
+              null;
+
+            // Vanilla JS node views are recreated on each update. However,
+            // using `ReactNodeViewRenderer` makes it so the node view is only
+            // created once, so the block we get in the node view will be
+            // outdated. Therefore, both variants have to (re-)resolve the
+            // block inside the `ReactNodeViewRenderer` component.
 
-            return ReactNodeViewRenderer(
-              (props: NodeViewProps) => {
-                // Vanilla JS node views are recreated on each update. However,
-                // using `ReactNodeViewRenderer` makes it so the node view is
-                // only created once, so the block we get in the node view will
-                // be outdated. Therefore, we have to get the block in the
-                // `ReactNodeViewRenderer` instead. That position can be stale,
-                // so resolving it is guarded (see `useNodeViewBlock`).
-                const block = useNodeViewBlock(props, initialBlock);
+            const ContainerNodeView = (props: NodeViewProps) => {
+              // Container blocks are bnBlock nodes (no `blockContainer`
+              // wrapper), so the id lives on the node's own attrs and the
+              // block resolves by id. Position-based resolution
+              // (`useNodeViewBlock`) would walk up to a *parent* bnBlock —
+              // the wrong block here — and ids are also immune to the stale
+              // positions it has to guard against.
+              const id = (props.node.attrs as Record<string, any>).id;
+              if (!id) {
+                throw new Error(
+                  `Container block "${blockConfig.type}" is missing an id attribute.`,
+                );
+              }
+              // The id lookup misses when the node was just removed from the
+              // document (e.g. a suggestion-mode deletion still rendering);
+              // fall back to converting the node the view was handed.
+              const block =
+                editor.getBlock(id) ??
+                nodeToBlock(props.node, props.view.state.doc);
+
+              const ref = useReactNodeView().nodeViewContentRef;
+              if (!ref) {
+                throw new Error("nodeViewContentRef is not set");
+              }
 
-                const ref = useReactNodeView().nodeViewContentRef;
+              const selected = props.selected;
 
-                if (!ref) {
-                  throw new Error("nodeViewContentRef is not set");
+              // Stamped imperatively rather than spread as JSX props: the root
+              // element belongs to the block's author, so there is nothing to
+              // spread onto. Runs after every render, since both the block's
+              // props and the author's root element can change.
+              useLayoutEffect(() => {
+                const root = authorRootDOM();
+                if (!root) {
+                  return;
                 }
 
-                const BlockContent = blockImplementation.render;
-                return (
-                  <BlockContentWrapper
-                    blockType={block.type}
-                    blockProps={block.props}
-                    propSchema={blockConfig.propSchema}
-                    isFileBlock={!!blockImplementation.meta?.fileBlockAccept}
-                    domAttributes={this.blockContentDOMAttributes}
-                  >
-                    <BlockContent
-                      block={block as any}
-                      editor={editor as any}
-                      contentRef={(element) => {
-                        ref(element);
-                        if (element) {
-                          element.className = mergeCSSClasses(
-                            "bn-inline-content",
-                            element.className,
-                          );
-                          element.dataset.nodeViewContent = "";
-                        }
-                      }}
-                    />
-                  </BlockContentWrapper>
+                applyContainerAttributes(
+                  root,
+                  blockConfig.type,
+                  block.props as any,
+                  blockConfig.propSchema,
+                  block.id,
                 );
-              },
-              {
-                className: "bn-react-node-view-renderer",
-              },
-            )(this.props!) as ReturnType<BlockImplementation["render"]>;
-          } else {
-            const BlockContent = blockImplementation.render;
-            const output = renderToDOMSpec((refCB) => {
+
+                // ProseMirror marks the outermost element with
+                // `ProseMirror-selectednode`, and that element carries
+                // `display: contents` for containers — which suppresses any
+                // outline drawn on it. So the state is mirrored onto the
+                // author's root, which is the block's actual box.
+                if (selected) {
+                  root.setAttribute("data-selected", "");
+                } else {
+                  root.removeAttribute("data-selected");
+                }
+              });
+
+              return (
+                <NodeViewWrapper ref={wrapper} style={DISPLAY_CONTENTS}>
+                  <BlockContent
+                    block={block as any}
+                    editor={editor as any}
+                    contentRef={(element: HTMLElement | null) => {
+                      ref(element);
+                      if (element) {
+                        element.dataset.nodeViewContent = "";
+                      }
+                    }}
+                  />
+                </NodeViewWrapper>
+              );
+            };
+
+            const RegularNodeView = (props: NodeViewProps) => {
+              // The node view's position can be stale mid-render, so
+              // resolving it is guarded (see `useNodeViewBlock`).
+              const block = useNodeViewBlock(props, initialBlock);
+
+              const ref = useReactNodeView().nodeViewContentRef;
+              if (!ref) {
+                throw new Error("nodeViewContentRef is not set");
+              }
+
               return (
                 <BlockContentWrapper
                   blockType={block.type}
                   blockProps={block.props}
                   propSchema={blockConfig.propSchema}
-                  domAttributes={this.blockContentDOMAttributes}
+                  isFileBlock={!!blockImplementation.meta?.fileBlockAccept}
+                  domAttributes={blockContentDOMAttributes}
                 >
                   <BlockContent
                     block={block as any}
                     editor={editor as any}
-                    contentRef={(element) => {
-                      refCB(element);
+                    contentRef={(element: HTMLElement | null) => {
+                      ref(element);
                       if (element) {
                         element.className = mergeCSSClasses(
                           "bn-inline-content",
                           element.className,
                         );
+                        element.dataset.nodeViewContent = "";
                       }
                     }}
                   />
                 </BlockContentWrapper>
               );
+            };
+
+            const nodeView = ReactNodeViewRenderer(
+              isContainer ? ContainerNodeView : RegularNodeView,
+              {
+                // The container class is separate because it *removes* the
+                // box the regular class relies on (see `Block.css`).
+                className: isContainer
+                  ? "bn-react-node-view-renderer bn-container-node-view"
+                  : "bn-react-node-view-renderer",
+              },
+            )(this.props!) as ReturnType<BlockImplementation["render"]>;
+
+            if (isContainer) {
+              // TipTap appends its content host into whichever element the
+              // block passed `contentRef` to. `display: contents` keeps that
+              // host from contributing a box, so the block's editable region
+              // lays out exactly where the author put the ref — and, for a
+              // container that has its own content, the content and children
+              // regions sit there as siblings.
+              if (nodeView.contentDOM) {
+                nodeView.contentDOM.style.display = "contents";
+              }
+              // Where core stamps the container attributes: the author's own
+              // element, not React's outermost wrapper (`dom`).
+              Object.defineProperty(nodeView, "rootDOM", {
+                get: authorRootDOM,
+              });
+            }
+
+            return nodeView;
+          } else {
+            const isContainer = isContainerType(blockConfig);
+            const BlockContent = blockImplementation.render as FC<any>;
+            const output = renderToDOMSpec((refCB) => {
+              const content = (
+                <BlockContent
+                  block={block as any}
+                  editor={editor as any}
+                  contentRef={(element: HTMLElement | null) => {
+                    refCB(element);
+                    if (element && !isContainer) {
+                      element.className = mergeCSSClasses(
+                        "bn-inline-content",
+                        element.className,
+                      );
+                    }
+                  }}
+                />
+              );
+              // See `toExternalHTML` above: a container block owns its outer
+              // DOM, so its render output is the block's root element.
+              return isContainer ? (
+                content
+              ) : (
+                <BlockContentWrapper
+                  blockType={block.type}
+                  blockProps={block.props}
+                  propSchema={blockConfig.propSchema}
+                  domAttributes={this.blockContentDOMAttributes}
+                >
+                  {content}
+                </BlockContentWrapper>
+              );
             }, editor);
             return output;
           }
diff --git a/packages/react/src/schema/useNodeViewBlock.ts b/packages/react/src/schema/useNodeViewBlock.ts
index 02393a2fd0..74d2e84037 100644
--- a/packages/react/src/schema/useNodeViewBlock.ts
+++ b/packages/react/src/schema/useNodeViewBlock.ts
@@ -42,6 +42,17 @@ export function useNodeViewBlock(
   const lastBlockRef = useRef(initialBlock);
   const doc = props.view.state.doc;
 
+  // Position-based resolution finds the nearest bnBlock *parent* of the
+  // position — correct for blockContent node views, but wrong-by-construction
+  // for container blocks, whose node IS the bnBlock: it would return an
+  // ancestor block. Guarded loudly so a container node view can't silently
+  // render the wrong block.
+  if (props.node.type.isInGroup("bnBlock")) {
+    throw new Error(
+      `useNodeViewBlock cannot resolve container block "${props.node.type.name}": position-based resolution returns the nearest bnBlock parent, which is the wrong block when the node view's node is the block itself. Resolve container blocks by id instead, e.g. editor.getBlock(props.node.attrs.id).`,
+    );
+  }
+
   try {
     // Deliberate render-phase write: a monotonic "last good value" cache, so a
     // repeated render (e.g. StrictMode's double invoke) recomputes the same
diff --git a/packages/react/vite.config.ts b/packages/react/vite.config.ts
index 2a835469db..ee43b8792d 100644
--- a/packages/react/vite.config.ts
+++ b/packages/react/vite.config.ts
@@ -1,7 +1,7 @@
 import react from "@vitejs/plugin-react";
 import * as path from "path";
 import { webpackStats } from "rollup-plugin-webpack-stats";
-import { defineConfig, type UserConfig } from "vite-plus";
+import { configDefaults, defineConfig, type UserConfig } from "vite-plus";
 import pkg from "./package.json";
 // import eslintPlugin from "vite-plugin-eslint";
 
@@ -24,6 +24,9 @@ export default defineConfig(
       test: {
         environment: "jsdom",
         setupFiles: ["./vitestSetup.ts"],
+        // `.browser.test` files need a real browser; the tests package's
+        // browser suite runs them.
+        exclude: [...configDefaults.exclude, "**/*.browser.test.*"],
       },
       plugins: [react(), webpackStats()],
       // used so that vitest resolves the core package from the sources instead of the built version
diff --git a/packages/react/vitestSetup.ts b/packages/react/vitestSetup.ts
index beafe25357..1c3619a84d 100644
--- a/packages/react/vitestSetup.ts
+++ b/packages/react/vitestSetup.ts
@@ -1,10 +1,21 @@
 import { afterEach, beforeEach } from "vite-plus/test";
 
+// This setup file also runs for test files that opt into the plain `node`
+// environment (`@vitest-environment node`), where there is no `window` at all —
+// everything below is a DOM mock, so it is a no-op there.
+const hasWindow = typeof window !== "undefined";
+
 beforeEach(() => {
+  if (!hasWindow) {
+    return;
+  }
   (window as Window & { __TEST_OPTIONS?: any }).__TEST_OPTIONS = {};
 });
 
 afterEach(() => {
+  if (!hasWindow) {
+    return;
+  }
   delete (window as Window & { __TEST_OPTIONS?: any }).__TEST_OPTIONS;
 });
 
@@ -32,28 +43,30 @@ class DragEventMock extends Event {
     },
   };
 }
-Object.defineProperty(window, "matchMedia", {
-  writable: true,
-  value: (query: string) => ({
-    matches: false,
-    media: query,
-    onchange: null,
-    addListener: () => {
-      //
-    }, // Deprecated
-    removeListener: () => {
-      //
-    }, // Deprecated
-    addEventListener: () => {
-      //
-    },
-    removeEventListener: () => {
-      //
-    },
-    dispatchEvent: () => {
-      //
-    },
-  }),
-});
+if (hasWindow) {
+  Object.defineProperty(window, "matchMedia", {
+    writable: true,
+    value: (query: string) => ({
+      matches: false,
+      media: query,
+      onchange: null,
+      addListener: () => {
+        //
+      }, // Deprecated
+      removeListener: () => {
+        //
+      }, // Deprecated
+      addEventListener: () => {
+        //
+      },
+      removeEventListener: () => {
+        //
+      },
+      dispatchEvent: () => {
+        //
+      },
+    }),
+  });
+}
 
 (global as any).DragEvent = DragEventMock;
diff --git a/packages/xl-ai/src/api/formats/html-blocks/collabUpdate.test.ts b/packages/xl-ai/src/api/formats/html-blocks/collabUpdate.test.ts
index fec31293a5..34d60aa6bf 100644
--- a/packages/xl-ai/src/api/formats/html-blocks/collabUpdate.test.ts
+++ b/packages/xl-ai/src/api/formats/html-blocks/collabUpdate.test.ts
@@ -80,7 +80,7 @@ function createCollabEditor(text: string) {
 function selectWholeFirstBlock(editor: BlockNoteEditor<any, any, any>) {
   const id = editor.document[0].id;
   const info = getBlockInfo(getNodeById(id, editor.prosemirrorState.doc)!);
-  if (!info.isBlockContainer) {
+  if (!info.isWrappedBlock) {
     throw new Error("not a block container");
   }
   const from = info.blockContent.beforePos + 1;
diff --git a/packages/xl-ai/src/prosemirror/agent.test.ts b/packages/xl-ai/src/prosemirror/agent.test.ts
index 44d87c8108..d2a7d9178b 100644
--- a/packages/xl-ai/src/prosemirror/agent.test.ts
+++ b/packages/xl-ai/src/prosemirror/agent.test.ts
@@ -39,7 +39,7 @@ describe.skip("getStepsAsAgent", () => {
     // Get the position of the content in the paragraph
     const blockPos = getNodeById("1", doc)!;
     const block = getBlockInfo(blockPos);
-    if (!block.isBlockContainer) {
+    if (!block.isWrappedBlock) {
       throw new Error("Block is not a container");
     }
 
@@ -72,7 +72,7 @@ describe.skip("getStepsAsAgent", () => {
     // Get the position of the content in the paragraph
     const blockPos = getNodeById("1", doc)!;
     const block = getBlockInfo(blockPos);
-    if (!block.isBlockContainer) {
+    if (!block.isWrappedBlock) {
       throw new Error("Block is not a container");
     }
 
@@ -98,7 +98,7 @@ describe.skip("getStepsAsAgent", () => {
     // Get the position of the content in the paragraph
     const blockPos = getNodeById("1", doc)!;
     const block = getBlockInfo(blockPos);
-    if (!block.isBlockContainer) {
+    if (!block.isWrappedBlock) {
       throw new Error("Block is not a container");
     }
 
@@ -128,7 +128,7 @@ describe.skip("getStepsAsAgent", () => {
     // Get the position of the content in the paragraph
     const blockPos = getNodeById("1", doc)!;
     const block = getBlockInfo(blockPos);
-    if (!block.isBlockContainer) {
+    if (!block.isWrappedBlock) {
       throw new Error("Block is not a container");
     }
 
@@ -157,7 +157,7 @@ describe.skip("getStepsAsAgent", () => {
     // Get the position of the content in the paragraph
     const blockPos = getNodeById("1", doc)!;
     const block = getBlockInfo(blockPos);
-    if (!block.isBlockContainer) {
+    if (!block.isWrappedBlock) {
       throw new Error("Block is not a container");
     }
 
diff --git a/packages/xl-ai/src/prosemirror/rebaseTool.test.ts b/packages/xl-ai/src/prosemirror/rebaseTool.test.ts
index 21454b7b79..edd8a3b1bb 100644
--- a/packages/xl-ai/src/prosemirror/rebaseTool.test.ts
+++ b/packages/xl-ai/src/prosemirror/rebaseTool.test.ts
@@ -21,7 +21,7 @@ function getExampleEditorWithSuggestions() {
   const blockPos = getNodeById("1", editor.prosemirrorState.doc)!;
 
   const block = getBlockInfo(blockPos);
-  if (!block.isBlockContainer) {
+  if (!block.isWrappedBlock) {
     throw new Error("Block is not a container");
   }
 
@@ -56,7 +56,7 @@ it("should be able to apply changes to a clean doc (use invertMap)", async () =>
 
   const block = getBlockInfo(blockPos);
 
-  if (!block.isBlockContainer) {
+  if (!block.isWrappedBlock) {
     throw new Error("Block is not a container");
   }
 
@@ -85,7 +85,7 @@ it("should be able to apply changes to a clean doc (use rebaseTr)", async () =>
 
   const block = getBlockInfo(blockPos);
 
-  if (!block.isBlockContainer) {
+  if (!block.isWrappedBlock) {
     throw new Error("Block is not a container");
   }
 
diff --git a/packages/xl-ai/src/testUtil/cases/combinedOperationsTestCases.ts b/packages/xl-ai/src/testUtil/cases/combinedOperationsTestCases.ts
index 6262f505cb..8bbcb29315 100644
--- a/packages/xl-ai/src/testUtil/cases/combinedOperationsTestCases.ts
+++ b/packages/xl-ai/src/testUtil/cases/combinedOperationsTestCases.ts
@@ -47,7 +47,7 @@ export const combinedOperationsTestCases: DocumentOperationTestCase[] = [
       const posInfo = getNodeById("ref2", editor.prosemirrorState.doc)!;
 
       const block = getBlockInfo(posInfo);
-      if (!block.isBlockContainer) {
+      if (!block.isWrappedBlock) {
         throw new Error("Block is not a block container");
       }
       return {
diff --git a/packages/xl-ai/src/testUtil/cases/updateOperationTestCases.ts b/packages/xl-ai/src/testUtil/cases/updateOperationTestCases.ts
index 2261863430..3d4d25f152 100644
--- a/packages/xl-ai/src/testUtil/cases/updateOperationTestCases.ts
+++ b/packages/xl-ai/src/testUtil/cases/updateOperationTestCases.ts
@@ -41,7 +41,7 @@ export const updateOperationTestCases: DocumentOperationTestCase[] = [
     getTestSelection: (editor: BlockNoteEditor<any, any, any>) => {
       const posInfo = getNodeById("ref2", editor.prosemirrorState.doc)!;
       const block = getBlockInfo(posInfo);
-      if (!block.isBlockContainer) {
+      if (!block.isWrappedBlock) {
         throw new Error("Block is not a block container");
       }
       return {
@@ -68,7 +68,7 @@ export const updateOperationTestCases: DocumentOperationTestCase[] = [
     getTestSelection: (editor: BlockNoteEditor<any, any, any>) => {
       const posInfo = getNodeById("ref1", editor.prosemirrorState.doc)!;
       const block = getBlockInfo(posInfo);
-      if (!block.isBlockContainer) {
+      if (!block.isWrappedBlock) {
         throw new Error("Block is not a block container");
       }
       // 'ello, world! Dow are yo'
@@ -737,7 +737,7 @@ export const updateOperationTestCases: DocumentOperationTestCase[] = [
     getTestSelection(editor) {
       const posInfo = getNodeById("ref2", editor.prosemirrorState.doc)!;
       const block = getBlockInfo(posInfo);
-      if (!block.isBlockContainer) {
+      if (!block.isWrappedBlock) {
         throw new Error("Block is not a block container");
       }
       return {
diff --git a/packages/xl-docx-exporter/src/docx/docxExporter.test.ts b/packages/xl-docx-exporter/src/docx/docxExporter.test.ts
index 16e45a304f..13b602ee91 100644
--- a/packages/xl-docx-exporter/src/docx/docxExporter.test.ts
+++ b/packages/xl-docx-exporter/src/docx/docxExporter.test.ts
@@ -1,5 +1,6 @@
 import {
   BlockNoteSchema,
+  createBlockSpec,
   defaultBlockSpecs,
   createPageBreakBlockSpec,
   PartialBlock,
@@ -415,6 +416,82 @@ describe("exporter", () => {
   );
 });
 
+describe("custom container blocks", () => {
+  const Box = createBlockSpec(
+    {
+      type: "box" as const,
+      propSchema: {},
+      content: "none",
+      children: { min: 1 },
+    },
+    {
+      render: (block: any) => {
+        const dom = document.createElement("div");
+        dom.setAttribute("data-node-type", "box");
+        dom.setAttribute("data-id", block.id);
+        return { dom, contentDOM: dom };
+      },
+    },
+  )();
+
+  const boxSchema = BlockNoteSchema.create({
+    blockSpecs: {
+      ...defaultBlockSpecs,
+      box: Box,
+    },
+  });
+
+  const boxDocument = partialBlocksToBlocksForTesting(boxSchema, [
+    {
+      type: "box",
+      children: [
+        { type: "paragraph", content: "First" },
+        { type: "paragraph", content: "Second" },
+      ],
+    },
+  ] as any);
+
+  it("passes children to a custom container mapping", async () => {
+    const exporter = new DOCXExporter(
+      boxSchema,
+      {
+        ...docxDefaultSchemaMappings,
+        blockMapping: {
+          ...docxDefaultSchemaMappings.blockMapping,
+          box: (
+            _block: any,
+            _exporter: any,
+            _nesting: any,
+            _index: any,
+            children: any,
+          ) =>
+            new Paragraph({
+              children: [new TextRun(`BOX(${children?.length ?? 0})`)],
+            }),
+        },
+      } as any,
+      { resolveFileUrl: testResolveFileUrl },
+    );
+
+    const transformed = await exporter.transformBlocks(boxDocument as any);
+    expect(transformed).toHaveLength(1);
+    const xml = JSON.stringify(transformed[0]);
+    expect(xml).toContain("BOX(2)");
+  });
+
+  it("throws a clear error for an unmapped container block", async () => {
+    const exporter = new DOCXExporter(
+      boxSchema,
+      docxDefaultSchemaMappings as any,
+      { resolveFileUrl: testResolveFileUrl },
+    );
+
+    await expect(exporter.transformBlocks(boxDocument as any)).rejects.toThrow(
+      /container block type "box"/,
+    );
+  });
+});
+
 function prettify(sourceXml: string) {
   let ret = xmlFormat(sourceXml);
 
diff --git a/packages/xl-docx-exporter/src/docx/docxExporter.ts b/packages/xl-docx-exporter/src/docx/docxExporter.ts
index f987ad4a7d..5caf6b5606 100644
--- a/packages/xl-docx-exporter/src/docx/docxExporter.ts
+++ b/packages/xl-docx-exporter/src/docx/docxExporter.ts
@@ -116,7 +116,7 @@ export class DOCXExporter<
     for (const b of blocks) {
       let children = await this.transformBlocks(b.children, nestingLevel + 1);
 
-      if (!["columnList", "column"].includes(b.type)) {
+      if (!this.isContainerBlock(b.type)) {
         children = children.map((c, _i) => {
           // NOTE: nested tables not supported (we can't insert the new Tab before a table)
           if (
@@ -139,7 +139,7 @@ export class DOCXExporter<
         0 /*unused*/,
         children,
       ); // TODO: any
-      if (["columnList", "column"].includes(b.type)) {
+      if (this.isContainerBlock(b.type)) {
         ret.push(self as Table);
       } else if (Array.isArray(self)) {
         ret.push(...self, ...children);
diff --git a/packages/xl-email-exporter/src/react-email/reactEmailExporter.tsx b/packages/xl-email-exporter/src/react-email/reactEmailExporter.tsx
index 5f4eecf3c5..df9fafdf61 100644
--- a/packages/xl-email-exporter/src/react-email/reactEmailExporter.tsx
+++ b/packages/xl-email-exporter/src/react-email/reactEmailExporter.tsx
@@ -246,6 +246,24 @@ export class ReactEmailExporter<
         i = nextIndex;
         continue;
       }
+      if (this.isContainerBlock(b.type)) {
+        // Container blocks (columnList, column, custom containers): the
+        // mapping owns the placement of the children, so they are passed in
+        // and not rendered as an indented sibling list.
+        const containerChildren = await this.transformBlocks(
+          b.children,
+          nestingLevel + 1,
+        );
+        const containerSelf = (await this.mapBlock(
+          b as any,
+          nestingLevel,
+          0,
+          containerChildren as any,
+        )) as any;
+        ret.push(<React.Fragment key={b.id}>{containerSelf}</React.Fragment>);
+        i++;
+        continue;
+      }
       // Non-list blocks
       const children = await this.transformBlocks(b.children, nestingLevel + 1);
       const self = (await this.mapBlock(b as any, nestingLevel, 0)) as any;
diff --git a/packages/xl-multi-column/src/blocks/Columns/index.ts b/packages/xl-multi-column/src/blocks/Columns/index.ts
index 2e49261ec6..1ffd9db2ee 100644
--- a/packages/xl-multi-column/src/blocks/Columns/index.ts
+++ b/packages/xl-multi-column/src/blocks/Columns/index.ts
@@ -1,28 +1,81 @@
+import { createBlockSpec } from "@blocknote/core";
+
+import { ColumnResizeExtension } from "../../extensions/ColumnResize/ColumnResizeExtension.js";
 import { MultiColumnDropHandlerExtension } from "../../extensions/DropCursor/multiColumnHandleDropPlugin.js";
-import { Column } from "../../pm-nodes/Column.js";
-import { ColumnList } from "../../pm-nodes/ColumnList.js";
 
-import { createBlockSpecFromTiptapNode } from "@blocknote/core";
+const COLUMN_WIDTH_DEFAULT = 1;
 
-export const ColumnBlock = createBlockSpecFromTiptapNode(
+export const ColumnBlock = createBlockSpec(
   {
-    node: Column,
-    type: "column",
+    type: "column" as const,
+    propSchema: {
+      width: {
+        default: COLUMN_WIDTH_DEFAULT,
+      },
+    },
     content: "none",
+    children: { exitOnEnter: false },
+    placement: "containerOnly",
   },
   {
-    width: {
-      default: 1,
+    meta: {
+      draggable: false,
+    },
+    render: (block) => {
+      const dom = document.createElement("div");
+      dom.className = "bn-block-column";
+      dom.style.flexGrow = String(block.props.width ?? COLUMN_WIDTH_DEFAULT);
+
+      return {
+        dom,
+        contentDOM: dom,
+        update: (newNode: {
+          type: { name: string };
+          attrs: { width?: number };
+        }) => {
+          if (newNode.type.name !== "column") {
+            return false;
+          }
+          dom.style.flexGrow = String(
+            newNode.attrs.width ?? COLUMN_WIDTH_DEFAULT,
+          );
+          return true;
+        },
+      };
     },
   },
-  [MultiColumnDropHandlerExtension()],
-);
+  [MultiColumnDropHandlerExtension(), ColumnResizeExtension()],
+)();
 
-export const ColumnListBlock = createBlockSpecFromTiptapNode(
+export const ColumnListBlock = createBlockSpec(
   {
-    node: ColumnList,
-    type: "columnList",
+    type: "columnList" as const,
+    propSchema: {},
     content: "none",
+    children: {
+      allow: { blocks: false, containers: ["column"] },
+      min: 2,
+      unwrapWhenEmptied: true,
+      exitOnEnter: false,
+    },
+  },
+  {
+    meta: {
+      isolating: false,
+      draggable: false,
+    },
+    render: () => {
+      const dom = document.createElement("div");
+      dom.className = "bn-block-column-list";
+      dom.style.display = "flex";
+
+      return {
+        dom,
+        contentDOM: dom,
+        update: (newNode: { type: { name: string } }) => {
+          return newNode.type.name === "columnList";
+        },
+      };
+    },
   },
-  {},
-);
+)();
diff --git a/packages/xl-multi-column/src/extensions/ColumnResize/ColumnResizeExtension.ts b/packages/xl-multi-column/src/extensions/ColumnResize/ColumnResizeExtension.ts
index 5713466a6d..2a6374c3e6 100644
--- a/packages/xl-multi-column/src/extensions/ColumnResize/ColumnResizeExtension.ts
+++ b/packages/xl-multi-column/src/extensions/ColumnResize/ColumnResizeExtension.ts
@@ -1,6 +1,5 @@
-import { BlockNoteEditor, getNodeById } from "@blocknote/core";
+import { BlockNoteEditor, createExtension, getNodeById } from "@blocknote/core";
 import { SideMenuExtension } from "@blocknote/core/extensions";
-import { Extension } from "@tiptap/core";
 import { Node } from "prosemirror-model";
 import { Plugin, PluginKey, PluginView } from "prosemirror-state";
 import { Decoration, DecorationSet, EditorView } from "prosemirror-view";
@@ -438,12 +437,7 @@ const createColumnResizePlugin = (editor: BlockNoteEditor<any, any, any>) =>
     view: (view) => new ColumnResizePluginView(editor, view),
   });
 
-export const createColumnResizeExtension = (
-  editor: BlockNoteEditor<any, any, any>,
-) =>
-  Extension.create({
-    name: "columnResize",
-    addProseMirrorPlugins() {
-      return [createColumnResizePlugin(editor)];
-    },
-  });
+export const ColumnResizeExtension = createExtension(({ editor }) => ({
+  key: "columnResize",
+  prosemirrorPlugins: [createColumnResizePlugin(editor)],
+}));
diff --git a/packages/xl-multi-column/src/extensions/DropCursor/multiColumnDropCursor.ts b/packages/xl-multi-column/src/extensions/DropCursor/multiColumnDropCursor.ts
index 77d93b7f4a..8f05068da3 100644
--- a/packages/xl-multi-column/src/extensions/DropCursor/multiColumnDropCursor.ts
+++ b/packages/xl-multi-column/src/extensions/DropCursor/multiColumnDropCursor.ts
@@ -1,4 +1,8 @@
-import { type DropCursorHooks, getNearestBlockPos } from "@blocknote/core";
+import {
+  type DropCursorHooks,
+  getNearestBlockPos,
+  isContainerNode,
+} from "@blocknote/core";
 import type { EditorState } from "prosemirror-state";
 import type { EditorView } from "prosemirror-view";
 
@@ -31,10 +35,16 @@ export function detectEdgePosition(
 
   const blockPos = getNearestBlockPos(state.doc, eventPos.pos);
 
-  // If we're at a block that's in a column, we want to compare the mouse position to the column, not the block inside it
-  // Why? Because we want to insert a new column in the columnList, instead of a new columnList inside of the column
+  // If we're at a block inside a column of a columnList, we want to compare
+  // the mouse position to the column, not the block inside it.
+  // Why? Because we want to insert a new sibling column in the columnList
+  // instead of a new container inside the column.
   let resolved = state.doc.resolve(blockPos.posBeforeNode);
-  if (resolved.parent.type.name === "column") {
+  if (
+    isContainerNode(resolved.parent.type) &&
+    resolved.depth > 0 &&
+    state.doc.resolve(resolved.before()).parent.type.name === "columnList"
+  ) {
     resolved = state.doc.resolve(resolved.before());
   }
 
diff --git a/packages/xl-multi-column/src/extensions/DropCursor/multiColumnHandleDropPlugin.ts b/packages/xl-multi-column/src/extensions/DropCursor/multiColumnHandleDropPlugin.ts
index a762f78d96..4d8b020ddd 100644
--- a/packages/xl-multi-column/src/extensions/DropCursor/multiColumnHandleDropPlugin.ts
+++ b/packages/xl-multi-column/src/extensions/DropCursor/multiColumnHandleDropPlugin.ts
@@ -4,6 +4,7 @@ import {
   createExtension,
   fragmentToBlocks,
   getBlockInfo,
+  isContainerNode,
   nodeToBlock,
 } from "@blocknote/core";
 import { Plugin } from "prosemirror-state";
@@ -42,7 +43,14 @@ export function createMultiColumnHandleDropPlugin(
         }
         const draggedBlockIds = new Set(draggedBlocks.map((block) => block.id));
 
-        if (blockInfo.blockNoteType === "column") {
+        // Whether the edge target is a `columnList` (after `detectEdgePosition`
+        // hoisted blocks inside a column to the column itself, the target's
+        // parent is the columnList).
+        const $target = view.state.doc.resolve(blockInfo.bnBlock.beforePos);
+        const targetInHorizontalContainer =
+          $target.node().type.name === "columnList";
+
+        if (targetInHorizontalContainer) {
           // The user is dropping the target column's entire contents on the
           // column's own edge - the new column would just replace the
           // emptied target in the same position, so do nothing. This also
@@ -57,16 +65,22 @@ export function createMultiColumnHandleDropPlugin(
             return true;
           }
 
-          // Insert new column in existing columnList
-          const parentBlock = view.state.doc
-            .resolve(blockInfo.bnBlock.beforePos)
-            .node();
+          // Insert a new sibling child in the existing horizontal container
+          // (e.g. a new column in the columnList).
+          const parentBlock = $target.node();
 
           const columnList = nodeToBlock<any, any, any>(
             parentBlock,
             view.state.doc,
           );
 
+          // Whether the horizontal container's children are typed child
+          // containers (like `column`) that wrap the actual blocks, or plain
+          // blocks spliced in directly.
+          const targetIsChildContainer = isContainerNode(
+            blockInfo.bnBlock.node.type,
+          );
+
           // Normalize column widths to average of 1
           // In a `columnList`, we expect that the average width of each column
           // is 1. However, there are cases in which this stops being true. For
@@ -74,24 +88,31 @@ export function createMultiColumnHandleDropPlugin(
           // the average width to go down. This isn't really an issue until the
           // user tries to add a new column, which will, in this case, be wider
           // than expected. Therefore, we normalize the column widths to an
-          // average of 1 here to avoid this issue.
-          let sumColumnWidthPercent = 0;
-          columnList.children.forEach((column) => {
-            sumColumnWidthPercent += column.props.width as number;
-          });
-          const avgColumnWidthPercent =
-            sumColumnWidthPercent / columnList.children.length;
-
-          // If the average column width is not 1, normalize it. We're dealing
-          // with floats so we need a small margin to account for precision
-          // errors.
-          if (avgColumnWidthPercent < 0.99 || avgColumnWidthPercent > 1.01) {
-            const scalingFactor = 1 / avgColumnWidthPercent;
-
+          // average of 1 here to avoid this issue. (Only applies to child
+          // containers with a numeric `width` prop, i.e. columns.)
+          if (
+            columnList.children.every(
+              (column) => typeof column.props.width === "number",
+            )
+          ) {
+            let sumColumnWidthPercent = 0;
             columnList.children.forEach((column) => {
-              column.props.width =
-                (column.props.width as number) * scalingFactor;
+              sumColumnWidthPercent += column.props.width as number;
             });
+            const avgColumnWidthPercent =
+              sumColumnWidthPercent / columnList.children.length;
+
+            // If the average column width is not 1, normalize it. We're
+            // dealing with floats so we need a small margin to account for
+            // precision errors.
+            if (avgColumnWidthPercent < 0.99 || avgColumnWidthPercent > 1.01) {
+              const scalingFactor = 1 / avgColumnWidthPercent;
+
+              columnList.children.forEach((column) => {
+                column.props.width =
+                  (column.props.width as number) * scalingFactor;
+              });
+            }
           }
 
           const targetColumnId = blockInfo.bnBlock.node.attrs.id;
@@ -103,20 +124,26 @@ export function createMultiColumnHandleDropPlugin(
           const remainingColumns = columnList.children
             // If any of the dragged blocks are in one of the columns, remove
             // them.
-            .map((column) => ({
-              ...column,
-              children: column.children.filter((block) => {
-                if (!draggedBlockIds.has(block.id)) {
-                  return true;
-                }
-
-                blocksAlreadyInColumnList.add(block.id);
-                return false;
-              }),
-            }))
+            .map((column) =>
+              targetIsChildContainer
+                ? {
+                    ...column,
+                    children: column.children.filter((block) => {
+                      if (!draggedBlockIds.has(block.id)) {
+                        return true;
+                      }
+
+                      blocksAlreadyInColumnList.add(block.id);
+                      return false;
+                    }),
+                  }
+                : column,
+            )
             // Remove empty columns (can happen when dragged blocks are
             // removed).
-            .filter((column) => column.children.length > 0);
+            .filter(
+              (column) => !targetIsChildContainer || column.children.length > 0,
+            );
 
           // The insertion index is computed on the remaining columns, as
           // removing an emptied column before the drop target shifts the
@@ -134,15 +161,22 @@ export function createMultiColumnHandleDropPlugin(
           const insertionIndex =
             edgePos.position === "left" ? targetIndex : targetIndex + 1;
 
-          // Insert the dragged blocks as a new column in the correct
-          // position.
-          const newChildren = remainingColumns.toSpliced(insertionIndex, 0, {
-            type: "column",
-            children: draggedBlocks,
-            props: {},
-            content: undefined,
-            id: UniqueID.options.generateID(),
-          });
+          // Insert the dragged blocks in the correct position, wrapped in a
+          // new child container (e.g. a new `column`) when the container's
+          // children are typed containers.
+          const newChildren = remainingColumns.toSpliced(
+            insertionIndex,
+            0,
+            targetIsChildContainer
+              ? {
+                  type: blockInfo.blockNoteType,
+                  children: draggedBlocks,
+                  props: {},
+                  content: undefined,
+                  id: UniqueID.options.generateID(),
+                }
+              : draggedBlocks[0],
+          );
 
           const blocksToRemove = draggedBlocks.filter(
             (block) =>
diff --git a/packages/xl-multi-column/src/pm-nodes/Column.ts b/packages/xl-multi-column/src/pm-nodes/Column.ts
deleted file mode 100644
index dccf60c74b..0000000000
--- a/packages/xl-multi-column/src/pm-nodes/Column.ts
+++ /dev/null
@@ -1,91 +0,0 @@
-import { suggestionMarks } from "@blocknote/core";
-import { Node } from "@tiptap/core";
-
-import { createColumnResizeExtension } from "../extensions/ColumnResize/ColumnResizeExtension.js";
-
-export const Column = Node.create({
-  name: "column",
-  group: "bnBlock childContainer",
-  // A block always contains content, and optionally a blockGroup which contains nested blocks
-  content: "blockContainer+",
-  priority: 40,
-  defining: true,
-  marks() {
-    return suggestionMarks(this.editor);
-  },
-  addAttributes() {
-    return {
-      width: {
-        // Why does each column have a default width of 1, i.e. 100%? Because
-        // when creating a new column, we want to make sure that existing
-        // column widths are preserved, while the new one also has a sensible
-        // width. If we'd set it so all column widths must add up to 100%
-        // instead, then each time a new column is created, we'd have to assign
-        // it a width depending on the total number of columns and also adjust
-        // the widths of the other columns. The same can be said for using px
-        // instead of percent widths and making them add to the editor width. So
-        // using this method is both simpler and computationally cheaper. This
-        // is possible because we can set the `flex-grow` property to the width
-        // value, which handles all the resizing for us, instead of manually
-        // having to set the `width` property of each column.
-        default: 1,
-        parseHTML: (element) => {
-          const attr = element.getAttribute("data-width");
-          if (attr === null) {
-            return null;
-          }
-
-          const parsed = parseFloat(attr);
-          if (isFinite(parsed)) {
-            return parsed;
-          }
-
-          return null;
-        },
-        renderHTML: (attributes) => {
-          return {
-            "data-width": (attributes.width as number).toString(),
-            style: `flex-grow: ${attributes.width as number};`,
-          };
-        },
-      },
-    };
-  },
-
-  parseHTML() {
-    return [
-      {
-        tag: "div",
-        getAttrs: (element) => {
-          if (typeof element === "string") {
-            return false;
-          }
-
-          if (element.getAttribute("data-node-type") === this.name) {
-            return {};
-          }
-
-          return false;
-        },
-      },
-    ];
-  },
-
-  renderHTML({ HTMLAttributes }) {
-    const column = document.createElement("div");
-    column.className = "bn-block-column";
-    column.setAttribute("data-node-type", this.name);
-    for (const [attribute, value] of Object.entries(HTMLAttributes)) {
-      column.setAttribute(attribute, value as any); // TODO as any
-    }
-
-    return {
-      dom: column,
-      contentDOM: column,
-    };
-  },
-
-  addExtensions() {
-    return [createColumnResizeExtension(this.options.editor)];
-  },
-});
diff --git a/packages/xl-multi-column/src/pm-nodes/ColumnList.ts b/packages/xl-multi-column/src/pm-nodes/ColumnList.ts
deleted file mode 100644
index eeb06f4d4e..0000000000
--- a/packages/xl-multi-column/src/pm-nodes/ColumnList.ts
+++ /dev/null
@@ -1,47 +0,0 @@
-import { suggestionMarks } from "@blocknote/core";
-import { Node } from "@tiptap/core";
-
-export const ColumnList = Node.create({
-  name: "columnList",
-  group: "childContainer bnBlock blockGroupChild",
-  // A block always contains content, and optionally a blockGroup which contains nested blocks
-  content: "column column+", // min two columns
-  priority: 40, // should be below blockContainer
-  defining: true,
-  marks() {
-    return suggestionMarks(this.editor);
-  },
-  parseHTML() {
-    return [
-      {
-        tag: "div",
-        getAttrs: (element) => {
-          if (typeof element === "string") {
-            return false;
-          }
-
-          if (element.getAttribute("data-node-type") === this.name) {
-            return {};
-          }
-
-          return false;
-        },
-      },
-    ];
-  },
-
-  renderHTML({ HTMLAttributes }) {
-    const columnList = document.createElement("div");
-    columnList.className = "bn-block-column-list";
-    columnList.setAttribute("data-node-type", this.name);
-    for (const [attribute, value] of Object.entries(HTMLAttributes)) {
-      columnList.setAttribute(attribute, value as any); // TODO as any
-    }
-    columnList.style.display = "flex";
-
-    return {
-      dom: columnList,
-      contentDOM: columnList,
-    };
-  },
-});
diff --git a/packages/xl-multi-column/src/test/commands/util/__snapshots__/fixColumnLists.test.ts.snap b/packages/xl-multi-column/src/test/commands/util/__snapshots__/fixContainer.test.ts.snap
similarity index 95%
rename from packages/xl-multi-column/src/test/commands/util/__snapshots__/fixColumnLists.test.ts.snap
rename to packages/xl-multi-column/src/test/commands/util/__snapshots__/fixContainer.test.ts.snap
index 87b5f2e588..a5d8ddf91f 100644
--- a/packages/xl-multi-column/src/test/commands/util/__snapshots__/fixColumnLists.test.ts.snap
+++ b/packages/xl-multi-column/src/test/commands/util/__snapshots__/fixContainer.test.ts.snap
@@ -1,6 +1,6 @@
 // Vitest Snapshot v1, https://vitest.dev/guide/snapshot.html
 
-exports[`Test fixColumnList > First of two columns empty 1`] = `
+exports[`Test fixContainer > First of two columns empty 1`] = `
 {
   "content": [
     {
@@ -35,7 +35,7 @@ exports[`Test fixColumnList > First of two columns empty 1`] = `
 }
 `;
 
-exports[`Test fixColumnList > Last of two columns empty 1`] = `
+exports[`Test fixContainer > Last of two columns empty 1`] = `
 {
   "content": [
     {
@@ -70,7 +70,7 @@ exports[`Test fixColumnList > Last of two columns empty 1`] = `
 }
 `;
 
-exports[`Test fixColumnList > Two empty columns 1`] = `
+exports[`Test fixContainer > Two empty columns 1`] = `
 {
   "content": [
     {
@@ -99,7 +99,7 @@ exports[`Test fixColumnList > Two empty columns 1`] = `
 }
 `;
 
-exports[`Test removeEmptyColumns > First of two columns empty 1`] = `
+exports[`Test removeEmptyChildren > First of two columns empty 1`] = `
 {
   "content": [
     {
@@ -176,7 +176,7 @@ exports[`Test removeEmptyColumns > First of two columns empty 1`] = `
 }
 `;
 
-exports[`Test removeEmptyColumns > Last of two columns empty 1`] = `
+exports[`Test removeEmptyChildren > Last of two columns empty 1`] = `
 {
   "content": [
     {
@@ -253,7 +253,7 @@ exports[`Test removeEmptyColumns > Last of two columns empty 1`] = `
 }
 `;
 
-exports[`Test removeEmptyColumns > Start and end columns empty 1`] = `
+exports[`Test removeEmptyChildren > Start and end columns empty 1`] = `
 {
   "content": [
     {
@@ -336,7 +336,7 @@ exports[`Test removeEmptyColumns > Start and end columns empty 1`] = `
 }
 `;
 
-exports[`Test removeEmptyColumns > Two empty columns 1`] = `
+exports[`Test removeEmptyChildren > Two empty columns 1`] = `
 {
   "content": [
     {
diff --git a/packages/xl-multi-column/src/test/commands/util/fixColumnLists.test.ts b/packages/xl-multi-column/src/test/commands/util/fixContainer.test.ts
similarity index 91%
rename from packages/xl-multi-column/src/test/commands/util/fixColumnLists.test.ts
rename to packages/xl-multi-column/src/test/commands/util/fixContainer.test.ts
index b5bd190c6d..d41cc00f72 100644
--- a/packages/xl-multi-column/src/test/commands/util/fixColumnLists.test.ts
+++ b/packages/xl-multi-column/src/test/commands/util/fixContainer.test.ts
@@ -2,14 +2,14 @@ import { describe, expect, it } from "vite-plus/test";
 
 import { setupTestEnv } from "../../setupTestEnv.js";
 import {
-  fixColumnList,
-  isEmptyColumn,
-  removeEmptyColumns,
-} from "@blocknote/core";
+  fixContainer,
+  isEmptyContainerChild,
+  removeEmptyChildren,
+} from "@blocknote/core/internal";
 
 const getEditor = setupTestEnv();
 
-describe("Test isEmptyColumn", () => {
+describe("Test isEmptyContainerChild", () => {
   it("Empty blocks", () => {
     const schema = getEditor()._tiptapEditor.schema;
 
@@ -19,7 +19,7 @@ describe("Test isEmptyColumn", () => {
       ]),
     ]);
 
-    expect(isEmptyColumn(column)).toBeTruthy();
+    expect(isEmptyContainerChild(column)).toBeTruthy();
   });
 
   it("Multiple blocks", () => {
@@ -34,7 +34,7 @@ describe("Test isEmptyColumn", () => {
       ]),
     ]);
 
-    expect(isEmptyColumn(column)).toBeFalsy();
+    expect(isEmptyContainerChild(column)).toBeFalsy();
   });
 
   it("Block with children", () => {
@@ -51,7 +51,7 @@ describe("Test isEmptyColumn", () => {
       ]),
     ]);
 
-    expect(isEmptyColumn(column)).toBeFalsy();
+    expect(isEmptyContainerChild(column)).toBeFalsy();
   });
 
   it("Block with text", () => {
@@ -65,7 +65,7 @@ describe("Test isEmptyColumn", () => {
       ]),
     ]);
 
-    expect(isEmptyColumn(column)).toBeFalsy();
+    expect(isEmptyContainerChild(column)).toBeFalsy();
   });
 
   it("Non-text block", () => {
@@ -77,11 +77,11 @@ describe("Test isEmptyColumn", () => {
       ]),
     ]);
 
-    expect(isEmptyColumn(column)).toBeFalsy();
+    expect(isEmptyContainerChild(column)).toBeFalsy();
   });
 });
 
-describe("Test removeEmptyColumns", () => {
+describe("Test removeEmptyChildren", () => {
   it("Start and end columns empty", () => {
     const editor = getEditor();
     const schema = editor._tiptapEditor.schema;
@@ -116,7 +116,7 @@ describe("Test removeEmptyColumns", () => {
     const tr = editor.prosemirrorState.tr;
 
     tr.replaceRangeWith(1, tr.doc.firstChild!.content.size, columnList);
-    removeEmptyColumns(tr, 1);
+    removeEmptyChildren(tr, 1);
 
     expect(tr.doc).toMatchSnapshot();
   });
@@ -143,7 +143,7 @@ describe("Test removeEmptyColumns", () => {
     const tr = editor.prosemirrorState.tr;
 
     tr.replaceRangeWith(1, tr.doc.firstChild!.content.size, columnList);
-    removeEmptyColumns(tr, 1);
+    removeEmptyChildren(tr, 1);
 
     expect(tr.doc).toMatchSnapshot();
   });
@@ -170,7 +170,7 @@ describe("Test removeEmptyColumns", () => {
     const tr = editor.prosemirrorState.tr;
 
     tr.replaceRangeWith(1, tr.doc.firstChild!.content.size, columnList);
-    removeEmptyColumns(tr, 1);
+    removeEmptyChildren(tr, 1);
 
     expect(tr.doc).toMatchSnapshot();
   });
@@ -195,13 +195,13 @@ describe("Test removeEmptyColumns", () => {
     const tr = editor.prosemirrorState.tr;
 
     tr.replaceRangeWith(1, tr.doc.firstChild!.content.size, columnList);
-    removeEmptyColumns(tr, 1);
+    removeEmptyChildren(tr, 1);
 
     expect(tr.doc).toMatchSnapshot();
   });
 });
 
-describe("Test fixColumnList", () => {
+describe("Test fixContainer", () => {
   it("First of two columns empty", () => {
     const editor = getEditor();
     const schema = editor._tiptapEditor.schema;
@@ -224,7 +224,7 @@ describe("Test fixColumnList", () => {
     const tr = editor.prosemirrorState.tr;
 
     tr.replaceRangeWith(1, tr.doc.firstChild!.content.size, columnList);
-    fixColumnList(tr, 1);
+    fixContainer(tr, 1);
 
     expect(tr.doc).toMatchSnapshot();
   });
@@ -251,7 +251,7 @@ describe("Test fixColumnList", () => {
     const tr = editor.prosemirrorState.tr;
 
     tr.replaceRangeWith(1, tr.doc.firstChild!.content.size, columnList);
-    fixColumnList(tr, 1);
+    fixContainer(tr, 1);
 
     expect(tr.doc).toMatchSnapshot();
   });
@@ -276,7 +276,7 @@ describe("Test fixColumnList", () => {
     const tr = editor.prosemirrorState.tr;
 
     tr.replaceRangeWith(1, tr.doc.firstChild!.content.size, columnList);
-    fixColumnList(tr, 1);
+    fixContainer(tr, 1);
 
     expect(tr.doc).toMatchSnapshot();
   });
diff --git a/packages/xl-multi-column/src/test/conversions/__snapshots__/multi-column/undefined/external.html b/packages/xl-multi-column/src/test/conversions/__snapshots__/multi-column/undefined/external.html
index 2237513b6b..72b0f2d7ab 100644
--- a/packages/xl-multi-column/src/test/conversions/__snapshots__/multi-column/undefined/external.html
+++ b/packages/xl-multi-column/src/test/conversions/__snapshots__/multi-column/undefined/external.html
@@ -1 +1 @@
-<div class="bn-block-column-list" data-node-type="columnList" data-id="1" style="display: flex;"><div class="bn-block-column" data-node-type="column" data-id="2" data-width="1" style="flex-grow: 1;" data-nesting-level="1"><p data-nesting-level="2">Column Paragraph 0</p><p data-nesting-level="2">Column Paragraph 1</p></div><div class="bn-block-column" data-node-type="column" data-id="5" data-width="1" style="flex-grow: 1;" data-nesting-level="1"><p data-nesting-level="2">Column Paragraph 2</p><p data-nesting-level="2">Column Paragraph 3</p></div></div>
\ No newline at end of file
+<div class="bn-block-column-list" style="display: flex;" data-node-type="columnList" data-id="1"><div class="bn-block-column" style="flex-grow: 1;" data-node-type="column" data-id="2" data-nesting-level="1"><p data-nesting-level="2">Column Paragraph 0</p><p data-nesting-level="2">Column Paragraph 1</p></div><div class="bn-block-column" style="flex-grow: 1;" data-node-type="column" data-id="5" data-nesting-level="1"><p data-nesting-level="2">Column Paragraph 2</p><p data-nesting-level="2">Column Paragraph 3</p></div></div>
\ No newline at end of file
diff --git a/packages/xl-multi-column/src/test/conversions/__snapshots__/multi-column/undefined/internal.html b/packages/xl-multi-column/src/test/conversions/__snapshots__/multi-column/undefined/internal.html
index 5876b3bd03..083e86c6ad 100644
--- a/packages/xl-multi-column/src/test/conversions/__snapshots__/multi-column/undefined/internal.html
+++ b/packages/xl-multi-column/src/test/conversions/__snapshots__/multi-column/undefined/internal.html
@@ -1 +1 @@
-<div class="bn-block-group" data-node-type="blockGroup"><div class="bn-block-column-list" data-node-type="columnList" data-id="1" style="display: flex;"><div class="bn-block-column" data-node-type="column" data-id="2" data-width="1" style="flex-grow: 1;"><div class="bn-block-outer" data-node-type="blockOuter" data-id="3"><div class="bn-block" data-node-type="blockContainer" data-id="3"><div class="bn-block-content" data-content-type="paragraph"><p class="bn-inline-content">Column Paragraph 0</p></div></div></div><div class="bn-block-outer" data-node-type="blockOuter" data-id="4"><div class="bn-block" data-node-type="blockContainer" data-id="4"><div class="bn-block-content" data-content-type="paragraph"><p class="bn-inline-content">Column Paragraph 1</p></div></div></div></div><div class="bn-block-column" data-node-type="column" data-id="5" data-width="1" style="flex-grow: 1;"><div class="bn-block-outer" data-node-type="blockOuter" data-id="6"><div class="bn-block" data-node-type="blockContainer" data-id="6"><div class="bn-block-content" data-content-type="paragraph"><p class="bn-inline-content">Column Paragraph 2</p></div></div></div><div class="bn-block-outer" data-node-type="blockOuter" data-id="7"><div class="bn-block" data-node-type="blockContainer" data-id="7"><div class="bn-block-content" data-content-type="paragraph"><p class="bn-inline-content">Column Paragraph 3</p></div></div></div></div></div></div>
\ No newline at end of file
+<div class="bn-block-group" data-node-type="blockGroup"><div class="bn-block-column-list" style="display: flex;" data-node-type="columnList" data-id="1"><div class="bn-block-column" style="flex-grow: 1;" data-node-type="column" data-id="2"><div class="bn-block-outer" data-node-type="blockOuter" data-id="3"><div class="bn-block" data-node-type="blockContainer" data-id="3"><div class="bn-block-content" data-content-type="paragraph"><p class="bn-inline-content">Column Paragraph 0</p></div></div></div><div class="bn-block-outer" data-node-type="blockOuter" data-id="4"><div class="bn-block" data-node-type="blockContainer" data-id="4"><div class="bn-block-content" data-content-type="paragraph"><p class="bn-inline-content">Column Paragraph 1</p></div></div></div></div><div class="bn-block-column" style="flex-grow: 1;" data-node-type="column" data-id="5"><div class="bn-block-outer" data-node-type="blockOuter" data-id="6"><div class="bn-block" data-node-type="blockContainer" data-id="6"><div class="bn-block-content" data-content-type="paragraph"><p class="bn-inline-content">Column Paragraph 2</p></div></div></div><div class="bn-block-outer" data-node-type="blockOuter" data-id="7"><div class="bn-block" data-node-type="blockContainer" data-id="7"><div class="bn-block-content" data-content-type="paragraph"><p class="bn-inline-content">Column Paragraph 3</p></div></div></div></div></div></div>
\ No newline at end of file
diff --git a/packages/xl-odt-exporter/src/odt/odtExporter.tsx b/packages/xl-odt-exporter/src/odt/odtExporter.tsx
index 7c17cad0ad..ee7bde9e60 100644
--- a/packages/xl-odt-exporter/src/odt/odtExporter.tsx
+++ b/packages/xl-odt-exporter/src/odt/odtExporter.tsx
@@ -142,7 +142,7 @@ export class ODTExporter<
         numberedListIndex = 0;
       }
 
-      if (["columnList", "column"].includes(block.type)) {
+      if (this.isContainerBlock(block.type)) {
         const children = await this.transformBlocks(block.children, 0);
         const content = await this.mapBlock(
           block as any,
diff --git a/packages/xl-pdf-exporter/src/pdf/pdfExporter.tsx b/packages/xl-pdf-exporter/src/pdf/pdfExporter.tsx
index f91ec93a86..1063ea5daa 100644
--- a/packages/xl-pdf-exporter/src/pdf/pdfExporter.tsx
+++ b/packages/xl-pdf-exporter/src/pdf/pdfExporter.tsx
@@ -176,7 +176,7 @@ export class PDFExporter<
         children,
       ); // TODO: any
 
-      if (["pageBreak", "columnList", "column"].includes(b.type)) {
+      if (b.type === "pageBreak" || this.isContainerBlock(b.type)) {
         ret.push(self);
         continue;
       }
diff --git a/playground/src/examples.gen.tsx b/playground/src/examples.gen.tsx
index 155a460786..9ff34c88ed 100644
--- a/playground/src/examples.gen.tsx
+++ b/playground/src/examples.gen.tsx
@@ -1457,6 +1457,33 @@ export const examples = {
         readme:
           "In this example, we create a custom block which renders a simple HTML paragraph with placeholder text. The block has no editable content.\n\n**Relevant Docs:**\n\n- [Custom Blocks](/docs/features/custom-schemas/custom-blocks)\n- [Editor Setup](/docs/getting-started/editor-setup)",
       },
+      {
+        projectSlug: "container-block",
+        fullSlug: "custom-schema/container-block",
+        pathFromRoot: "examples/06-custom-schema/09-container-block",
+        config: {
+          playground: true,
+          docs: true,
+          author: "nickthesick",
+          tags: [
+            "Intermediate",
+            "Blocks",
+            "Custom Schemas",
+            "Suggestion Menus",
+            "Slash Menu",
+          ],
+          dependencies: {
+            "react-icons": "^5.5.0",
+          } as any,
+        },
+        title: "Container Block",
+        group: {
+          pathFromRoot: "examples/06-custom-schema",
+          slug: "custom-schema",
+        },
+        readme:
+          'In this example, we create a custom `Callout` block that holds **other blocks** as its body — like a Notion-style callout that can wrap a paragraph followed by a code block, or any combination of nested blocks.\n\nThe block declares the `children` config on `BlockConfig`. `children: { min: 1, default: [{ type: "paragraph" }] }` makes it a container: its child blocks mount into the element the render passes `contentRef` to, and live on `block.children` at runtime.\n\nThe callout\'s **title** demonstrates the complementary "string prop slot" pattern: a field that doesn\'t need rich text, comments, or multiplayer cursors can live in a plain string prop, edited through a regular `<input>` rendered inside the block (in a `contentEditable={false}` wrapper) and committed via `editor.updateBlock`. A field that _is_ prose belongs in the block\'s own `content: "inline"` instead.\n\nWe also wire up a Slash Menu item to insert the callout, and render the document JSON next to the editor so you can inspect the structure of the nested blocks.\n\n**Try it out:**\n\n- Press the "/" key inside the callout\'s body and add a code block, heading, or list — anything goes.\n- Type a title into the title field — it\'s stored on `block.props.title`, not as document content.\n- Watch the JSON panel on the right update as you edit; the callout\'s children appear in `block.children`.\n- Insert a new callout via the Slash Menu (search "callout").\n\n**Relevant Docs:**\n\n- [Container Blocks](/docs/features/custom-schemas/container-blocks)\n- [Custom Blocks](/docs/features/custom-schemas/custom-blocks)\n- [Editor Setup](/docs/getting-started/editor-setup)',
+      },
       {
         projectSlug: "math-block",
         fullSlug: "custom-schema/math-block",
@@ -1536,6 +1563,33 @@ export const examples = {
         readme:
           'In this example, we build custom blocks on the source-with-preview pattern — the same building blocks behind BlockNote\'s math and diagram blocks. A custom "CSV table" block renders its comma-separated source as a table, and a custom "color" inline content renders a CSS color as a swatch. Both show the rendered preview in place, while the source is edited in a popup.\n\n**Try it out:** Click the table or a color chip to edit its source!\n\n**Relevant Docs:**\n\n- [Source with Preview Blocks](/docs/features/custom-schemas/source-with-preview)\n- [Custom Blocks](/docs/features/custom-schemas/custom-blocks)\n- [Custom Inline Content](/docs/features/custom-schemas/custom-inline-content)',
       },
+      {
+        projectSlug: "table-container",
+        fullSlug: "custom-schema/table-container",
+        pathFromRoot: "examples/06-custom-schema/12-table-container",
+        config: {
+          playground: true,
+          docs: false,
+          author: "nickthesick",
+          tags: [
+            "Advanced",
+            "Blocks",
+            "Custom Schemas",
+            "Suggestion Menus",
+            "Slash Menu",
+          ],
+          dependencies: {
+            "react-icons": "^5.5.0",
+          } as any,
+        },
+        title: "Table From Container Blocks",
+        group: {
+          pathFromRoot: "examples/06-custom-schema",
+          slug: "custom-schema",
+        },
+        readme:
+          "In this example, we build a table out of three nested container blocks — `gridTable > gridRow > gridCell` — instead of a `content: \"table\"` block. The whole nesting structure comes from each block's `children` config, so the document schema enforces it, and because a cell's `children` allows any block, cells can hold lists, headings, code blocks, or another table.\n\nThe blocks render real `<table>` / `<tr>` / `<td>` elements: a container block owns its outer DOM, so `contentRef` / `contentDOM` places its children directly inside. They're written with the vanilla `createBlockSpec` rather than `createReactBlockSpec` for exactly that reason — a React block renders through a `NodeViewWrapper` div, and a `<div>` between a `<table>` and its rows gives you a table that looks right but isn't one to the DOM.\n\nWhat the container API can't express is the grid _semantics_: nothing in `children` can say \"every row has the same number of cells\", so the row/column buttons and the Tab navigation are ordinary code written against `insertBlocks` / `removeBlocks`. Column spans, rectangular cell selection, and column resizing aren't implemented at all.\n\n**Try it out:**\n\n- Type in a cell, then press Tab and Shift-Tab to move between cells — Tab past the last cell adds a row.\n- Use the `+ Row` / `+ Column` buttons below a table, and watch the shape readout next to them.\n- Press \"/\" inside a cell and insert a heading, list, or even another Grid Table.\n- Watch the JSON panel: a table is just `gridTable > gridRow > gridCell` in `block.children`.\n\n**Relevant Docs:**\n\n- [Container Blocks](/docs/features/custom-schemas/container-blocks)\n- [Custom Blocks](/docs/features/custom-schemas/custom-blocks)\n- [Editor Setup](/docs/getting-started/editor-setup)",
+      },
       {
         projectSlug: "draggable-inline-content",
         fullSlug: "custom-schema/draggable-inline-content",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 6decb347ed..cbcf97aa1e 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -3459,6 +3459,52 @@ importers:
         specifier: ^8.0.0
         version: 8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0)
 
+  examples/06-custom-schema/09-container-block:
+    dependencies:
+      '@blocknote/ariakit':
+        specifier: latest
+        version: link:../../../packages/ariakit
+      '@blocknote/core':
+        specifier: latest
+        version: link:../../../packages/core
+      '@blocknote/mantine':
+        specifier: latest
+        version: link:../../../packages/mantine
+      '@blocknote/react':
+        specifier: latest
+        version: link:../../../packages/react
+      '@blocknote/shadcn':
+        specifier: latest
+        version: link:../../../packages/shadcn
+      '@mantine/core':
+        specifier: ^9.0.2
+        version: 9.1.1(@mantine/hooks@9.1.1(react@19.2.5))(@types/react@19.2.14)(react-dom@19.2.5(react@19.2.5))(react@19.2.5)
+      '@mantine/hooks':
+        specifier: ^9.0.2
+        version: 9.1.1(react@19.2.5)
+      react:
+        specifier: ^19.2.3
+        version: 19.2.5
+      react-dom:
+        specifier: ^19.2.3
+        version: 19.2.5(react@19.2.5)
+      react-icons:
+        specifier: ^5.5.0
+        version: 5.6.0(react@19.2.5)
+    devDependencies:
+      '@types/react':
+        specifier: ^19.2.3
+        version: 19.2.14
+      '@types/react-dom':
+        specifier: ^19.2.3
+        version: 19.2.3(@types/react@19.2.14)
+      '@vitejs/plugin-react':
+        specifier: ^6.0.1
+        version: 6.0.1(babel-plugin-react-compiler@1.0.0)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))
+      vite-plus:
+        specifier: ^0.1.24
+        version: 0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(vitest@4.1.10)(yaml@2.9.0)
+
   examples/06-custom-schema/09-math-block:
     dependencies:
       '@blocknote/ariakit':
@@ -3609,6 +3655,52 @@ importers:
         specifier: ^8.0.0
         version: 8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0)
 
+  examples/06-custom-schema/12-table-container:
+    dependencies:
+      '@blocknote/ariakit':
+        specifier: latest
+        version: link:../../../packages/ariakit
+      '@blocknote/core':
+        specifier: latest
+        version: link:../../../packages/core
+      '@blocknote/mantine':
+        specifier: latest
+        version: link:../../../packages/mantine
+      '@blocknote/react':
+        specifier: latest
+        version: link:../../../packages/react
+      '@blocknote/shadcn':
+        specifier: latest
+        version: link:../../../packages/shadcn
+      '@mantine/core':
+        specifier: ^9.0.2
+        version: 9.1.1(@mantine/hooks@9.1.1(react@19.2.5))(@types/react@19.2.14)(react-dom@19.2.5(react@19.2.5))(react@19.2.5)
+      '@mantine/hooks':
+        specifier: ^9.0.2
+        version: 9.1.1(react@19.2.5)
+      react:
+        specifier: ^19.2.3
+        version: 19.2.5
+      react-dom:
+        specifier: ^19.2.3
+        version: 19.2.5(react@19.2.5)
+      react-icons:
+        specifier: ^5.5.0
+        version: 5.6.0(react@19.2.5)
+    devDependencies:
+      '@types/react':
+        specifier: ^19.2.3
+        version: 19.2.14
+      '@types/react-dom':
+        specifier: ^19.2.3
+        version: 19.2.3(@types/react@19.2.14)
+      '@vitejs/plugin-react':
+        specifier: ^6.0.1
+        version: 6.0.1(babel-plugin-react-compiler@1.0.0)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))
+      vite-plus:
+        specifier: ^0.1.24
+        version: 0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(vitest@4.1.10)(yaml@2.9.0)
+
   examples/06-custom-schema/draggable-inline-content:
     dependencies:
       '@blocknote/ariakit':
@@ -5115,9 +5207,9 @@ importers:
       '@vitejs/plugin-react':
         specifier: ^6.0.1
         version: 6.0.1(babel-plugin-react-compiler@1.0.0)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))
-      vite:
-        specifier: ^8.0.0
-        version: 8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0)
+      vite-plus:
+        specifier: ^0.1.24
+        version: 0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(vitest@4.1.10)(yaml@2.9.0)
 
   packages/ariakit:
     dependencies:
@@ -8220,6 +8312,10 @@ packages:
     resolution: {integrity: sha512-a61ljmRVVyG5MC/698C8/FfFDw5a8LOIvyOLW5fztgUXqUpc1jOfQzOitSCbge657OgXXThmY3Tk8fpiDb4UcA==}
     engines: {node: '>= 20.0.0'}
 
+  '@oxc-project/runtime@0.133.0':
+    resolution: {integrity: sha512-PkvjA1Lq5++V5S1E6Patr92ZVcieE6EalDr1VJTqv4BnjZdOUC4W3p8k1wMXSd5/2aFP4b/A6N5sg2Bkzcr9vQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+
   '@oxc-project/runtime@0.143.0':
     resolution: {integrity: sha512-zIuXUf+YGIgsPk0xlQmzTY8NCSc8jE/pSfDodlQ9H3EGZABmr+AtIjXRrnpQAXuXzhDSNqZz9cuhud8hDDLvpg==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8227,51 +8323,103 @@ packages:
   '@oxc-project/types@0.124.0':
     resolution: {integrity: sha512-VBFWMTBvHxS11Z5Lvlr3IWgrwhMTXV+Md+EQF0Xf60+wAdsGFTBx7X7K/hP4pi8N7dcm1RvcHwDxZ16Qx8keUg==}
 
+  '@oxc-project/types@0.133.0':
+    resolution: {integrity: sha512-KzkdCd6Uxqnf6l3HOw1xfatAlUURA0g14cvBYFyJ5SaNOQbOUvBr9PKArcPcrNIeRsBdgcUzOGrhKveVpvOIGA==}
+
   '@oxc-project/types@0.143.0':
     resolution: {integrity: sha512-u6JZdLBTLotrNC9Vd6vPssINdzcCzleKAH6EJKImQb7GtYvX5keN2dxkoK44stCc4tffE6QQRtZTXVSzsLUlWA==}
 
+  '@oxfmt/binding-android-arm-eabi@0.52.0':
+    resolution: {integrity: sha512-17EMSJnQ9g+upVHrAUYDMfH5lvRKQ9Nvg8WtEoH72oDr1VpWz+7/o3tD97U1EToen2YAQ/68JmtDYkQUi20dfQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm]
+    os: [android]
+
   '@oxfmt/binding-android-arm-eabi@0.62.0':
     resolution: {integrity: sha512-pdsv0C4gPjJ8H1+sd8u0BDx+yLACTL+rgeMIOL1ln4ihSnhw8CWXtYWgvcSkyTfgGBIzFKab+d8rx9Xl4en/Kw==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm]
     os: [android]
 
+  '@oxfmt/binding-android-arm64@0.52.0':
+    resolution: {integrity: sha512-A2G1IdwGEW2lLJkIxcvuirRH1CzSl/e0NX11zTlW1gvxJThfwbI/BEoaKrTNpm7M2FchvIf6guvIQU7d5iz+OQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [android]
+
   '@oxfmt/binding-android-arm64@0.62.0':
     resolution: {integrity: sha512-WC3YQ7uS/KtDrjmqwBviwFKe9qeoi+eXx8aX1z/ffG23Md75myjrJaQqTuJvdOLPoa4EYTjDWH0dHXfwulCVog==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm64]
     os: [android]
 
+  '@oxfmt/binding-darwin-arm64@0.52.0':
+    resolution: {integrity: sha512-f9+bLvOYxy7NttCLFTvQ7afmqDOWY4wIP9xdvfj5trQ1qj6f2UFAGwZESlfsMjvJNTyRpXfIlOanCI9FOvoeQA==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [darwin]
+
   '@oxfmt/binding-darwin-arm64@0.62.0':
     resolution: {integrity: sha512-GM8Yf3LjjaR1I8PD0SfeoIlwhsh9GvSF+cQ8sf624Yxnjsyumn95aFzYfKJVefblfDIiOAnZ7QVm2sa21Er/0Q==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm64]
     os: [darwin]
 
+  '@oxfmt/binding-darwin-x64@0.52.0':
+    resolution: {integrity: sha512-YSTB9sJ5nnQd/Q0ddHkgof0ZCHPAnWZT1IW2SJ8omz7CP7KluJhO1fNHrpqdxCtpztJwSs4hY1uAee35wKxxaw==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [darwin]
+
   '@oxfmt/binding-darwin-x64@0.62.0':
     resolution: {integrity: sha512-d5THp7F8bCxLqNogEXDORRsQD6dosf3EyFtnXfBer6v+8tGdcWIjoDX9WaXrrF/26zOmL8qHpPTKCEvpBDmZkQ==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [x64]
     os: [darwin]
 
+  '@oxfmt/binding-freebsd-x64@0.52.0':
+    resolution: {integrity: sha512-NIrRNTTPCs4UbmVs0bxLSCDlLCtIRMJIXklNKaXa5Oj2/K1UIMBvgE8+uPVo01Io3N9HF0+GAX+aAHjUgZS7vA==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [freebsd]
+
   '@oxfmt/binding-freebsd-x64@0.62.0':
     resolution: {integrity: sha512-1DnrtXGZooOZ0fHgAXZUaDQzBVh1CM2MNW4oBXyQ2aWKvCHjyljvT9fgBkOM0fEOb96X5eqtcfJ0YUVt9jj66g==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [x64]
     os: [freebsd]
 
+  '@oxfmt/binding-linux-arm-gnueabihf@0.52.0':
+    resolution: {integrity: sha512-JXUCde8mn3GpgQouz2PXUokgy/uT1QrRJBL2s983VWcSQp62wTFYiNXgTKdeo1Jgbr0IgUnKKvzIk/YBlj/nVQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm]
+    os: [linux]
+
   '@oxfmt/binding-linux-arm-gnueabihf@0.62.0':
     resolution: {integrity: sha512-4pQDHOYRH+Huqe0StIaWyvk2CVl/aTaqSrbZpA3/pLS2xH24ME7lBgYprhQF2fRkHBzhGGGKliwxFsDdHwx59g==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm]
     os: [linux]
 
+  '@oxfmt/binding-linux-arm-musleabihf@0.52.0':
+    resolution: {integrity: sha512-psbUXaRZ+V8DaXz10Qf7LSHtdtdKAmC8fxXgeU608jjzrmWK4quamZMOpl6sf+dikoFHA85uE93Q0BqxrCdQrQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm]
+    os: [linux]
+
   '@oxfmt/binding-linux-arm-musleabihf@0.62.0':
     resolution: {integrity: sha512-X0jAaZJFMCVKhB6YyWVTQ/wN2DLsBcZKSMqTS76bF6riT+XZdtg2FPEdjDvdVbunO9cG+tWiVaEs4Zs38lxYog==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm]
     os: [linux]
 
+  '@oxfmt/binding-linux-arm64-gnu@0.52.0':
+    resolution: {integrity: sha512-Jw7MgWUU9lcLCcy82updISP3EthTlfvAwR6gWNxPzqly7+fLvOi2gHQE9xXQjpqaVLm/8P+gOzlv9ODuoVlaaw==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [linux]
+    libc: [glibc]
+
   '@oxfmt/binding-linux-arm64-gnu@0.62.0':
     resolution: {integrity: sha512-682Z8T5s8T5ATArYtsejKvbIfd8LEAXyyDkKkoZVq8HND7Vx8TYLlrDjDSeYfodMeVwHOgkj13lJYR8cj6vUSg==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8279,6 +8427,13 @@ packages:
     os: [linux]
     libc: [glibc]
 
+  '@oxfmt/binding-linux-arm64-musl@0.52.0':
+    resolution: {integrity: sha512-wZg6bLjDvh2KibyI3QFUYo8GTXneIFsd0JvehtvJiUmQ8WRPERgxd/VM4ctWb86U5FT1FkqgS8/wZKVB+AZScg==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [linux]
+    libc: [musl]
+
   '@oxfmt/binding-linux-arm64-musl@0.62.0':
     resolution: {integrity: sha512-lk25fAl7KWaLWVJcW0CHEXB7QlQZtx5eDkjpaGMK0hzXTjUe0Wmlu8IKuFHoviSOcEJedRTs4VE/506VqGxGew==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8286,6 +8441,13 @@ packages:
     os: [linux]
     libc: [musl]
 
+  '@oxfmt/binding-linux-ppc64-gnu@0.52.0':
+    resolution: {integrity: sha512-IngE8uxhNvxcMrLjZNDo9xNLY7rEK33AKnaMd2B46he1e/mz2CfcW6If/U1wUjdRZddm1QzQaciqZkuMkdh1FA==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [ppc64]
+    os: [linux]
+    libc: [glibc]
+
   '@oxfmt/binding-linux-ppc64-gnu@0.62.0':
     resolution: {integrity: sha512-SFyNqHQLwySceWNLhiSldx7wPXRAzP0L0WcW9GegP3uWrpZGJiZlQO85NbHAFPEfxR9PhZ9qSnZryEh7+v+4Gw==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8293,6 +8455,13 @@ packages:
     os: [linux]
     libc: [glibc]
 
+  '@oxfmt/binding-linux-riscv64-gnu@0.52.0':
+    resolution: {integrity: sha512-H3+DdFMv/efN3Efmhsv18jDrpiWWqKG7wsfAlQBqAt6z/E2Bx+TwEj2Nowe51CPOWB8/mFBC2dAMSgVFLvvowA==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [riscv64]
+    os: [linux]
+    libc: [glibc]
+
   '@oxfmt/binding-linux-riscv64-gnu@0.62.0':
     resolution: {integrity: sha512-KYj55C1ywJfHo6+aKDuEmUtVEdJALsC5GwayDGsI6FGz2GxFqNr/mA8nxVsNbJzm7sE5MRqTQ9ziImSzhYXysA==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8300,6 +8469,13 @@ packages:
     os: [linux]
     libc: [glibc]
 
+  '@oxfmt/binding-linux-riscv64-musl@0.52.0':
+    resolution: {integrity: sha512-zji+1kb7lJKohSDjzC1IsS+K/cKRs1hdVf0ZH0VbdbiakmtLvN9twBoXo/k8VdjFax7kfo+DyPxS7vv52br1aw==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [riscv64]
+    os: [linux]
+    libc: [musl]
+
   '@oxfmt/binding-linux-riscv64-musl@0.62.0':
     resolution: {integrity: sha512-BhZDNo5GOU5nC378RhD0/XpvaEBHsH3HLgJp8YZX3A0InC7oivzA63HsRmiXFLtLSHAstEVrDf6fbC7Rs8Jh/A==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8307,6 +8483,13 @@ packages:
     os: [linux]
     libc: [musl]
 
+  '@oxfmt/binding-linux-s390x-gnu@0.52.0':
+    resolution: {integrity: sha512-hcLBYedpCy7ToUvvBidWk7+11Yhg1oAZ4+6hKPic/mQI6NaqXJSXMps5nFlwUuX2ewhtLZZDPg63TI042qGKBg==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [s390x]
+    os: [linux]
+    libc: [glibc]
+
   '@oxfmt/binding-linux-s390x-gnu@0.62.0':
     resolution: {integrity: sha512-UyAFmyHkgSgUJ/wOM4p3U8AC2yAFvRH5PNBs7TnK0fObTT/XSWcdr/lAzPSWaekHaZFaMeFZyk9n93Joq3J93A==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8314,6 +8497,13 @@ packages:
     os: [linux]
     libc: [glibc]
 
+  '@oxfmt/binding-linux-x64-gnu@0.52.0':
+    resolution: {integrity: sha512-IDO2loXK2OtTOhSPchU9MW25mWL2QCDGdJbjN8MXKZVS80qXe5gMTwQWu/gMJ3juoBHbkuUZNB2N1LHzNT7DoA==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [linux]
+    libc: [glibc]
+
   '@oxfmt/binding-linux-x64-gnu@0.62.0':
     resolution: {integrity: sha512-1iYMP0leytWazFubD/WnINJuIrzRPuoL1aWEJdlGezEzDbTxcd29R4r8IUzP2oWeKst5V02uMJgR2NILlPlG6w==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8321,6 +8511,13 @@ packages:
     os: [linux]
     libc: [glibc]
 
+  '@oxfmt/binding-linux-x64-musl@0.52.0':
+    resolution: {integrity: sha512-mAV2Hjn0SatJ+KoAzKUC3eJhdJ8wv+3m1KyuS0dTsbF0c5weq+QrCt/DRZZM+uj/XiKzCDEUKYsBF30e2qkcyw==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [linux]
+    libc: [musl]
+
   '@oxfmt/binding-linux-x64-musl@0.62.0':
     resolution: {integrity: sha512-4rA/URtJSTVNVAQz6Q8wf7SaRvOXVy+TizriT9hs/Y1XhLR/R+92uWKRQG8yFWRAIEBbFHJ6WevQcl/G9SXEfw==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8328,102 +8525,205 @@ packages:
     os: [linux]
     libc: [musl]
 
+  '@oxfmt/binding-openharmony-arm64@0.52.0':
+    resolution: {integrity: sha512-vd4npaUIwChxp7XzkqmepBWTT9YMcSe/NBApVGPC30/lLyOVaV3dvma1SKo03t8O73BPRAG7EyJzGlN5cJM5hQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [openharmony]
+
   '@oxfmt/binding-openharmony-arm64@0.62.0':
     resolution: {integrity: sha512-mSZuFHU2ar1KLUjXpI2QBQcJ1VsOB3mOCgQXuXCpKs19dgh4u+OaovNfrWDfiJb+ihJ2+f7YFcaO9bS2dlTCXA==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm64]
     os: [openharmony]
 
+  '@oxfmt/binding-win32-arm64-msvc@0.52.0':
+    resolution: {integrity: sha512-k2sz6gWQdMfh5HPpIS+Bw/0UEV/kaK2xuqJRrWL233sEHx9WLlsmvlPFM4HUNThkYbSN0U0vPW7LVKZWDS8hPQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [win32]
+
   '@oxfmt/binding-win32-arm64-msvc@0.62.0':
     resolution: {integrity: sha512-OfwuhkcjDlqC4EgDojtiV9mzpLqeB9KqTOWPOjLEYBVdDCVSxqW3qzp/xcIxsbtI0UgGCnKvAqYKyY25kf5JZw==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm64]
     os: [win32]
 
+  '@oxfmt/binding-win32-ia32-msvc@0.52.0':
+    resolution: {integrity: sha512-rhke69GTcArodLHpjMTfNnvjTEBryDeZcUCKK/VjXDMtfTULl6QRh0ymX5/hbCUv2WjYm9h/QbW++q2vE15gWQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [ia32]
+    os: [win32]
+
   '@oxfmt/binding-win32-ia32-msvc@0.62.0':
     resolution: {integrity: sha512-P9uDDNFRzghO3X8QAzhkjKhK7JvtABsVn8UYtFX7uor12IAnwNt8nNIctvfWj1JkQU/kE+fmLRPiw7XlrIHsZw==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [ia32]
     os: [win32]
 
+  '@oxfmt/binding-win32-x64-msvc@0.52.0':
+    resolution: {integrity: sha512-q5xL7oeXkZdEtNZWBdvehJcmt+GRu9l2bK40yJs1jJXlqq+r0Hygb1rTjq+FM2o/2xyt4cufH6KRplHp3Jjsvw==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [win32]
+
   '@oxfmt/binding-win32-x64-msvc@0.62.0':
     resolution: {integrity: sha512-dlI5SY7XYQCiCBafntWagCR6HcAJB/NpsLtdlPx8x08+Osz8Ok1HHz1GZuusegCe/VoJ6pAnF5a4pd5OZAq7qQ==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [x64]
     os: [win32]
 
+  '@oxlint-tsgolint/darwin-arm64@0.23.0':
+    resolution: {integrity: sha512-gOs9PVr2wEg4ox9z0aJo+RKhhImW86YL5N6yav8BK/rgPsIrwN/igSZ+pbRr723NFvUNKde9fgMhRA6JrXAOZw==}
+    cpu: [arm64]
+    os: [darwin]
+
   '@oxlint-tsgolint/darwin-arm64@7.0.2001':
     resolution: {integrity: sha512-CUJEdbSZ54+Xy9OXqOhWLTKZKV0BBiV7C2i/ygyVmXtkUNXx5YCzN8DpSSshTAKktoL7S+tnQ/ftFG/i7X896w==}
     cpu: [arm64]
     os: [darwin]
 
+  '@oxlint-tsgolint/darwin-x64@0.23.0':
+    resolution: {integrity: sha512-kjJ8B+7n4tB9VJdxS5A9GdJt6/bYpzbu4lXp2uO1S3sRmCB5gDEABlGoiePNApRWaW+xqL4b4xgiE727jSLhuA==}
+    cpu: [x64]
+    os: [darwin]
+
   '@oxlint-tsgolint/darwin-x64@7.0.2001':
     resolution: {integrity: sha512-pXfBb5BqONCcgrXQNUZWXgiYmRSWJzd97S8i41VVOh6ut0tyo+cJ5FKFpczDHxiVNfj/3e7c9B4MtztNdpIVCw==}
     cpu: [x64]
     os: [darwin]
 
+  '@oxlint-tsgolint/linux-arm64@0.23.0':
+    resolution: {integrity: sha512-6dCZuKNu135seMXilkRk9SpCx6i1XgmiipYGalLij5WVRX6ZYS8c4xI7preN/zv9fCXhsQclTIMDu2Y/cytTjw==}
+    cpu: [arm64]
+    os: [linux]
+
   '@oxlint-tsgolint/linux-arm64@7.0.2001':
     resolution: {integrity: sha512-roP7zujb/QDPzDwEKsFFpzNHHy91/Y7oX9vQXk78ekyZtcQj1QXDIMH33gjDdHBfRl4K9pZ36xhRgrP4Zr+R8A==}
     cpu: [arm64]
     os: [linux]
 
+  '@oxlint-tsgolint/linux-x64@0.23.0':
+    resolution: {integrity: sha512-3bdilnyA7kmSTjK27rvjIjSxL5SIg3wt7vwNiRkouWB83ytssyKnuGvxSYJxgMEmFpSutzaBzcCUM2jDtPGcgA==}
+    cpu: [x64]
+    os: [linux]
+
   '@oxlint-tsgolint/linux-x64@7.0.2001':
     resolution: {integrity: sha512-UDezNqdECVmngu2TPnjaS1YoAmcTaBoI5lV9vk3VahBxoi+I5r9k3iJTT7qZoYWOXTD/7T7bNcwRgrocR6BscQ==}
     cpu: [x64]
     os: [linux]
 
+  '@oxlint-tsgolint/win32-arm64@0.23.0':
+    resolution: {integrity: sha512-j+OEp44SVYiQ+ZD+uttsX7u6L9SvmbbQ77SO1pSFCcJlsVMeCk8qZsjhKfGKuT/jIA+ipOJMVs/+pqUfObBWNw==}
+    cpu: [arm64]
+    os: [win32]
+
   '@oxlint-tsgolint/win32-arm64@7.0.2001':
     resolution: {integrity: sha512-uJZhqB6pdXLuN+AD1F5082byyQti/NPmJA77GtcFlmT2HzRelqbNls3SaIqxpjdFgvSBF9g0yOKGBkGFg7kX8Q==}
     cpu: [arm64]
     os: [win32]
 
+  '@oxlint-tsgolint/win32-x64@0.23.0':
+    resolution: {integrity: sha512-5MyjFuqf+g8OUPJBSGWHJtmoWnzFJYyOg4To9WMQshZYEWig/vtu7JtJ03VWnzHv9LJkAUeApY0gVCOywFR/iQ==}
+    cpu: [x64]
+    os: [win32]
+
   '@oxlint-tsgolint/win32-x64@7.0.2001':
     resolution: {integrity: sha512-FkDRm8hx9OwzGQqyWG1tO5QrTLRApff9DzSgpz9QZau37BR8d1VYKOxMLGf6shPZntJFoTwIIJYT68VndYDCog==}
     cpu: [x64]
     os: [win32]
 
+  '@oxlint/binding-android-arm-eabi@1.67.0':
+    resolution: {integrity: sha512-VrSi571rDv1N8HaEDM+DEX8nmT0y9jJo8tzzW13vsOWTx59xQczCIJx68n2zWOXRT5YKZsOZXp4qkHN/10x4mw==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm]
+    os: [android]
+
   '@oxlint/binding-android-arm-eabi@1.77.0':
     resolution: {integrity: sha512-E06sKWS6PiI6HRxS1wyQg22HvApt01hI7fV+T3wUk3OSbaaP4a3hYGY/MIQDmASqCiRjBdpRQYkgMkqH82cWmQ==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm]
     os: [android]
 
+  '@oxlint/binding-android-arm64@1.67.0':
+    resolution: {integrity: sha512-l6+NdYxMoRohix5r5bbigW16LPicceCwGcQ6LKKuE1kUdjgFfQolJjrJsQYPFetIs78Gxj/G/f5TEGoTCwj9nQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [android]
+
   '@oxlint/binding-android-arm64@1.77.0':
     resolution: {integrity: sha512-NvsKz0KZxTp9cYWPLf+FXaSZwB3oO3peAjtukpOMBgse2vhQSoIIVqeO1yR0lEo/UcdZIDL18uq+kL0LzQ0ytA==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm64]
     os: [android]
 
+  '@oxlint/binding-darwin-arm64@1.67.0':
+    resolution: {integrity: sha512-jOzXxS1AxFxhImLIRbtGIMrEwaXcgMw3gR57WB1cRk8ai+vpr6726kxXqVvlNsrXtJ/FrmOm8RxlC0m8SW24Qg==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [darwin]
+
   '@oxlint/binding-darwin-arm64@1.77.0':
     resolution: {integrity: sha512-bgjTn6nW4bQCFBvSvuHCpDD+sONvmpo4lGI4PxzMt1quBA+xYxhczk6RiCn3GZ9gY8uhaBbwhj9MdKGfu6T9DA==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm64]
     os: [darwin]
 
+  '@oxlint/binding-darwin-x64@1.67.0':
+    resolution: {integrity: sha512-3DFAVY94OqjIZHXIPz37yGRSWwOFTAqChQ64/M69GYLawzP0KiwdhDNfqdKKYT0bTR/DNxmMnQsj3ns+8+X/Lg==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [darwin]
+
   '@oxlint/binding-darwin-x64@1.77.0':
     resolution: {integrity: sha512-aotaIttH1R6j1Rwhx0M0htgeZyGtVQqYNTVEYMN/UcgHPquGA6kmk9OyuDc3a2GKUQBC+3C3GVQCcrRPMYqAFA==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [x64]
     os: [darwin]
 
+  '@oxlint/binding-freebsd-x64@1.67.0':
+    resolution: {integrity: sha512-e4dDKZuLu8TR9DEBssWSDahlPgZBwojTTHZUvnjBRJfJJbpxYCjfjKfi0Z1+CSLMiJBwI2yCDtRM1XJQaARjmg==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [freebsd]
+
   '@oxlint/binding-freebsd-x64@1.77.0':
     resolution: {integrity: sha512-nNx/wta7ksRAdYvq+l4AWjXkLxEXHALhENxjj2cYbQAIR4ybaA5L+hCbE63HOmft5czQ6ks+hb8vmEAnn7YGPg==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [x64]
     os: [freebsd]
 
+  '@oxlint/binding-linux-arm-gnueabihf@1.67.0':
+    resolution: {integrity: sha512-BKytFdcQzbITV3xlnzDUDTEDtbUMCCiC4EaNTDZ4FyT8gdNvBC4gfiLucXp/sQl0XU3p7syTlorUWVVVBZab2g==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm]
+    os: [linux]
+
   '@oxlint/binding-linux-arm-gnueabihf@1.77.0':
     resolution: {integrity: sha512-tMLLjM7xXtzXisVCzkOTXNCy9bZVId2wteNwjohlFDR/jY6WagpEDA1c1wu4xRc20Hojaxj+V6DSR7gbKxijWA==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm]
     os: [linux]
 
+  '@oxlint/binding-linux-arm-musleabihf@1.67.0':
+    resolution: {integrity: sha512-XYAv0esBDX7BpTzRDjVX2Vdj+zndd8ll2dFQiaeQ6zTZr7A8GRDTN7fH3FP3jU+O0vCDx85oH/EtG7BzPgAXuw==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm]
+    os: [linux]
+
   '@oxlint/binding-linux-arm-musleabihf@1.77.0':
     resolution: {integrity: sha512-MiAFDFaqR0tmHTAyo0YDcZ5hyLREdYw/RQhc2R3cbT+8O3tB+zqPM2th9TTQ+Uo3jn/embS+DO+HyX9ztCPkOQ==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm]
     os: [linux]
 
+  '@oxlint/binding-linux-arm64-gnu@1.67.0':
+    resolution: {integrity: sha512-zizRMjA0i6u/2B0evgda04iycu+MoNuf1pBy6Eh+1CjC5wMEG7qN5zdDKTCvFc0KSYSDM9QTG3gjZHirgtQuKg==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [linux]
+    libc: [glibc]
+
   '@oxlint/binding-linux-arm64-gnu@1.77.0':
     resolution: {integrity: sha512-/xqQ3B16i1T4cyt/9Mn+4CpzhUXoBXp7kVpIwzOXNFLj5JmK1bIjsbSnX296Gg8A/o7oDtKWikFgBx0SLwztkw==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8431,6 +8731,13 @@ packages:
     os: [linux]
     libc: [glibc]
 
+  '@oxlint/binding-linux-arm64-musl@1.67.0':
+    resolution: {integrity: sha512-zB/Tf6sUjmmvvbva9Gj3JTJ8rJ9t4I8/U0o6vSRtd0DRIsIuyegBwJAzhSUFQHdMijIRJkW0exs/yBhpw2S20w==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [linux]
+    libc: [musl]
+
   '@oxlint/binding-linux-arm64-musl@1.77.0':
     resolution: {integrity: sha512-LSbwuRKiNCenPDcbARqAZ5RfBy7gmj7vOvfJRLeCDU3gFtSxWbhv/+VTlaUqzUhNj1gFLHB8h7ALnxa/Az6z6g==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8438,6 +8745,13 @@ packages:
     os: [linux]
     libc: [musl]
 
+  '@oxlint/binding-linux-ppc64-gnu@1.67.0':
+    resolution: {integrity: sha512-kgU40Gt74CK0TCsF51KZymkIwN9U0BajKsMijB52zPqOeZU9NAHkA/NSQkZDHEaCakx42DxhXkODiAqf2b4Gug==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [ppc64]
+    os: [linux]
+    libc: [glibc]
+
   '@oxlint/binding-linux-ppc64-gnu@1.77.0':
     resolution: {integrity: sha512-QWdcH31mXEUe5Nq1s0CfCpceaKjIo9uZtwDjAuL681g1axf+5x8xrg/eXWaw//4NCxYZ4V4e5Hu5tvdR+pTBlg==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8445,6 +8759,13 @@ packages:
     os: [linux]
     libc: [glibc]
 
+  '@oxlint/binding-linux-riscv64-gnu@1.67.0':
+    resolution: {integrity: sha512-tOYhkk/iaG9aD3FvGpBFd1Lrw0x0RaVoJBxjUkfNzS50rC5NS5BteNCwgr8A2zCdADrIIoze6D7u6U5Ic++/iQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [riscv64]
+    os: [linux]
+    libc: [glibc]
+
   '@oxlint/binding-linux-riscv64-gnu@1.77.0':
     resolution: {integrity: sha512-GnOfYgJxbcElOiPZaDFDl406ONddwvOWk2jvAAAEjwAl4GofNoHF+/HHUIBYa6bFCArlcGPi0XjC4cU1pkgF/Q==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8452,6 +8773,13 @@ packages:
     os: [linux]
     libc: [glibc]
 
+  '@oxlint/binding-linux-riscv64-musl@1.67.0':
+    resolution: {integrity: sha512-sEtywrPb+0b+tHYl1SDCrw903fiC4eyKoNqzP3v+f2JT3Xcv4NEYG+P8rj+eEnX7IWhqV/xj8/JmcmVj21CXaA==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [riscv64]
+    os: [linux]
+    libc: [musl]
+
   '@oxlint/binding-linux-riscv64-musl@1.77.0':
     resolution: {integrity: sha512-AyEMTUCf0xY+hHF+IxqXFQIX0yQOIR8ykpY0lJNOw9xYqOzUX8dyZfRvlG0RfXwuQn2eonf/8NrMmDSZJjdqsA==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8459,6 +8787,13 @@ packages:
     os: [linux]
     libc: [musl]
 
+  '@oxlint/binding-linux-s390x-gnu@1.67.0':
+    resolution: {integrity: sha512-BvR8Moa0zCLxroOx4vZaZN9nUfwAUpSTwjZdxZyKy4bv3PrzrXrxKR/ZQ0L9wNSvlPhnMJeZfa3q5w6ZCTuN6Q==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [s390x]
+    os: [linux]
+    libc: [glibc]
+
   '@oxlint/binding-linux-s390x-gnu@1.77.0':
     resolution: {integrity: sha512-sPLzEcNvxd/oyVQ5oZo92CiHkFkpBeRop13E/P3TPY+hZfXHKCOWKI70TE2RYwMKFJDc20EMjH16L7NZICtKTw==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8466,6 +8801,13 @@ packages:
     os: [linux]
     libc: [glibc]
 
+  '@oxlint/binding-linux-x64-gnu@1.67.0':
+    resolution: {integrity: sha512-mm2cxM6fksOpq6l0uFws8BUGKAR4dNa/cZCn37Npq7PFbhD5HDJqWfnoIvTaeRKMy5XdS2tO0MA0qbHDrnXAAA==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [linux]
+    libc: [glibc]
+
   '@oxlint/binding-linux-x64-gnu@1.77.0':
     resolution: {integrity: sha512-1Oh2ssH2L7lwyvkdSqaMUfsGfwU2Wfvew+obBUYjRVqhpBcUpwnsPSEr1IzVi9XqkuY10geiLsNKecqaZC34Dw==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8473,6 +8815,13 @@ packages:
     os: [linux]
     libc: [glibc]
 
+  '@oxlint/binding-linux-x64-musl@1.67.0':
+    resolution: {integrity: sha512-WmbMuLapKyDlobMkXAaAL0Y+Uczh4LETfIfQsUpbId4Ip8Ai82/jqeYTOoUCkuuhBFapgqP253+d83tLKOksJg==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [linux]
+    libc: [musl]
+
   '@oxlint/binding-linux-x64-musl@1.77.0':
     resolution: {integrity: sha512-0j/2wRgNGO+Qj/M1uu/p57h/hFTTWWcfie0ufkbabeus2s5+/QqkCflnMOwLLN5m2GsNeWp4xdl4cPa4n7QCOQ==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -8480,30 +8829,58 @@ packages:
     os: [linux]
     libc: [musl]
 
+  '@oxlint/binding-openharmony-arm64@1.67.0':
+    resolution: {integrity: sha512-9g/PqxYJelzzTAOR5Y+RiRqdeydhEuXv2KxNeFcAKQ7UsvnWSY1OP4MsuPMbTO2Pf70tz7mFhl1j13H3fyh+8g==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [openharmony]
+
   '@oxlint/binding-openharmony-arm64@1.77.0':
     resolution: {integrity: sha512-BJ/j54qS0usEnyDkLYURMj2iiD9h5Cyy+ppzeMSXBGRXaGRNWnj1Mw14NqWMR5E/PzdgB30OOCCzLzbRoduafw==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm64]
     os: [openharmony]
 
+  '@oxlint/binding-win32-arm64-msvc@1.67.0':
+    resolution: {integrity: sha512-2VhwE6Gatb0vJGnN0TBuQMbKCOiZlSQ/zJvVWYLK4a9d4iDiJOen/yVQkGpmsJ90MuH66fzi0kEKI0jRQMDxGA==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [win32]
+
   '@oxlint/binding-win32-arm64-msvc@1.77.0':
     resolution: {integrity: sha512-Yh8w+g2Lpx7StrvtYkoz9JJvXjB9wxgFChFNb85nrXm/wj/XTwGWS1hve9+900HL7llrntYB3YP+y32E3tRqzA==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm64]
     os: [win32]
 
+  '@oxlint/binding-win32-ia32-msvc@1.67.0':
+    resolution: {integrity: sha512-EQ3VExXfeM1InbE5+JjufhZZTWy+kHUwgt3yZR7gQ47Je/mE0WspQPan0OJznh493L5anM210YNJtH1PXjTSFg==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [ia32]
+    os: [win32]
+
   '@oxlint/binding-win32-ia32-msvc@1.77.0':
     resolution: {integrity: sha512-zja5b7+6a7UsRFgAQSrnax5vrzliEyNPLCjfXONu/vTWswaIVZGFajJZptaeRvPE4LghtFdAzVFlexTm7MVTGA==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [ia32]
     os: [win32]
 
+  '@oxlint/binding-win32-x64-msvc@1.67.0':
+    resolution: {integrity: sha512-bw24y+/1MHS4QDkons3YyHkPT9uCMoLHHgQhb+mb8NOjTYwub1CZ+K9Ngr8aO5DMrDrkqHwTzlTwFP2vS8Y/ZQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [win32]
+
   '@oxlint/binding-win32-x64-msvc@1.77.0':
     resolution: {integrity: sha512-+teyvPDZ2RjUvo+SuCqS/UhaJl1QtdW5fWT5NJTV61V5MIuIS90Db9LixmtEGvXixyttiK62P96MSu3UlpviBw==}
     engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [x64]
     os: [win32]
 
+  '@oxlint/plugins@1.61.0':
+    resolution: {integrity: sha512-nkOyZEF1vH527CkdQtOp1HMrVFEM4ResURvI2JFeGoup+h+43J/k/FgdOR9b9Isxg+Yae7qVDa7y3nssE8b3TQ==}
+    engines: {node: ^12.22.0 || ^14.17.0 || >=16.0.0}
+
   '@oxlint/plugins@1.73.0':
     resolution: {integrity: sha512-OhgMQeMmZA0dcFcX4/priaJZWdFECxiClgq6mRX6aatZEcV9PbKC3P3/v8U1hVjviT1i5U+vR8lAtBV6m4FXAA==}
     engines: {node: ^12.22.0 || ^14.17.0 || >=16.0.0}
@@ -11265,6 +11642,69 @@ packages:
   '@vitest/utils@4.1.5':
     resolution: {integrity: sha512-76wdkrmfXfqGjueGgnb45ITPyUi1ycZ4IHgC2bhPDUfWHklY/q3MdLOAB+TF1e6xfl8NxNY0ZYaPCFNWSsw3Ug==}
 
+  '@voidzero-dev/vite-plus-core@0.1.24':
+    resolution: {integrity: sha512-iXPGBABnQnrDMx89H6MOCGcTZp+QW+3rY4YMVKdE6ydchSvPk2O3MI2vgaRVfOtWJ2IjnxSnf1n2yjP67ZBRFQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    peerDependencies:
+      '@arethetypeswrong/core': ^0.18.1
+      '@tsdown/css': 0.22.1
+      '@tsdown/exe': 0.22.1
+      '@types/node': ^25.6.0
+      '@vitejs/devtools': ^0.1.18
+      esbuild: ^0.27.0 || ^0.28.0
+      jiti: '>=1.21.0'
+      less: ^4.0.0
+      publint: ^0.3.8
+      sass: ^1.70.0
+      sass-embedded: ^1.70.0
+      stylus: '>=0.54.8'
+      sugarss: ^5.0.0
+      terser: ^5.16.0
+      tsx: ^4.8.1
+      typescript: ^5.0.0 || ^6.0.0
+      unplugin-unused: ^0.5.0
+      unrun: '*'
+      yaml: ^2.4.2
+    peerDependenciesMeta:
+      '@arethetypeswrong/core':
+        optional: true
+      '@tsdown/css':
+        optional: true
+      '@tsdown/exe':
+        optional: true
+      '@types/node':
+        optional: true
+      '@vitejs/devtools':
+        optional: true
+      esbuild:
+        optional: true
+      jiti:
+        optional: true
+      less:
+        optional: true
+      publint:
+        optional: true
+      sass:
+        optional: true
+      sass-embedded:
+        optional: true
+      stylus:
+        optional: true
+      sugarss:
+        optional: true
+      terser:
+        optional: true
+      tsx:
+        optional: true
+      typescript:
+        optional: true
+      unplugin-unused:
+        optional: true
+      unrun:
+        optional: true
+      yaml:
+        optional: true
+
   '@voidzero-dev/vite-plus-core@0.2.9':
     resolution: {integrity: sha512-dWqScAAwa8h/i9jCiGAMs7YarzQWInHZ5gCJNbQkHXA6Zp6A2T2anN9YMFVPpb7CwVFwkI2iPF5yl/DXtq+zUA==}
     engines: {node: ^20.19.0 || ^22.18.0 || >=24.11.0}
@@ -11322,18 +11762,37 @@ packages:
       yaml:
         optional: true
 
+  '@voidzero-dev/vite-plus-darwin-arm64@0.1.24':
+    resolution: {integrity: sha512-Hpo9W9piSFlEsJzGkwzfDXhJGrnYByxHXF7NVQZ7g+SLOprddtlfTeM8t+gq9dxcuq0RzM8ddMAhDQP/K3fZQA==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [darwin]
+
   '@voidzero-dev/vite-plus-darwin-arm64@0.2.9':
     resolution: {integrity: sha512-/qJHqMfyy/LiCJk4UYZfFW6Comsfm8zDuy4P8UFWnFqRjmefYvZbMK4ThYNM87tKNWYWjsnClzssjJOmDTAc8w==}
     engines: {node: '>=20.0.0'}
     cpu: [arm64]
     os: [darwin]
 
+  '@voidzero-dev/vite-plus-darwin-x64@0.1.24':
+    resolution: {integrity: sha512-SwnnnZrEFBiU5iKlh/CZAVwn0RFt/Udrvt3kFLtdRxMtN5bKaqTFVA2H8Y/FPCWp1QX9bs4V9ZIAeXAk06zLkw==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [darwin]
+
   '@voidzero-dev/vite-plus-darwin-x64@0.2.9':
     resolution: {integrity: sha512-3MGnNeazgYAqQTaC7JIbZyrTHmxSXTWFr9G1yAdeItKasB1R8HKIkCS1Qnr49Ge4S/cyOODivdbcpqFkrT93ng==}
     engines: {node: '>=20.0.0'}
     cpu: [x64]
     os: [darwin]
 
+  '@voidzero-dev/vite-plus-linux-arm64-gnu@0.1.24':
+    resolution: {integrity: sha512-ImM3eqDki4DpRuHjW6dEh4St8zvbcfOMR7KQZJX42ArriCLQ/QdaYhDRRbcDi27XsOBqRxm2eqUUEymPrYIHpA==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [linux]
+    libc: [glibc]
+
   '@voidzero-dev/vite-plus-linux-arm64-gnu@0.2.9':
     resolution: {integrity: sha512-6LmukER8qD4UBIRqMNv4Ilq7CxfRhngLUXlMv8vbTupeLRWPJSKvKEHyRxCwr6JP57Gxfr8KrX1ye42WzcZF0g==}
     engines: {node: '>=20.0.0'}
@@ -11341,26 +11800,84 @@ packages:
     os: [linux]
     libc: [glibc]
 
-  '@voidzero-dev/vite-plus-linux-arm64-musl@0.2.9':
-    resolution: {integrity: sha512-cBs626GWkyJlwKP0nsdHlMWpuTl9xOWRxAUoqtxXPtw80bVy4WM5eNS4SXPC5pX10jR7DRIkRpzNAsy7fv8Faw==}
-    engines: {node: '>=20.0.0'}
+  '@voidzero-dev/vite-plus-linux-arm64-musl@0.1.24':
+    resolution: {integrity: sha512-gj4mzbob/ls8Zs7iTuF9Gr0EFFF7tdpDiPxDPBkH8tJP5OkHABlzWUwJhU+9xxcUbTaXqpHDw68Mil7jm5dpMg==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [arm64]
+    os: [linux]
+    libc: [musl]
+
+  '@voidzero-dev/vite-plus-linux-arm64-musl@0.2.9':
+    resolution: {integrity: sha512-cBs626GWkyJlwKP0nsdHlMWpuTl9xOWRxAUoqtxXPtw80bVy4WM5eNS4SXPC5pX10jR7DRIkRpzNAsy7fv8Faw==}
+    engines: {node: '>=20.0.0'}
+    cpu: [arm64]
+    os: [linux]
+    libc: [musl]
+
+  '@voidzero-dev/vite-plus-linux-x64-gnu@0.1.24':
+    resolution: {integrity: sha512-x7IYK7lI+WuF1n3jSzEYU6FgJxPX/R0rDmTTsOutooGGCU7uShZvfZqIoiTXK0eFnJU5ij5BfBgenenUfsaT/A==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [linux]
+    libc: [glibc]
+
+  '@voidzero-dev/vite-plus-linux-x64-gnu@0.2.9':
+    resolution: {integrity: sha512-2Iy8x4PCPMNzXeu3pREevlggoeK8PwtdUiCpoSybAZBtR/aqMxsJREyt/eKv45F8lsiNlA8PbIWEvPxLSgzFLQ==}
+    engines: {node: '>=20.0.0'}
+    cpu: [x64]
+    os: [linux]
+    libc: [glibc]
+
+  '@voidzero-dev/vite-plus-linux-x64-musl@0.1.24':
+    resolution: {integrity: sha512-JCy2w0eSVUlWQlggK5T47MnL+j0o4EY7hLskINVI8gi+aixQF4xnYBDobz0lbxkqz3/IfiLyXUx6TcU3thcsGQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [linux]
+    libc: [musl]
+
+  '@voidzero-dev/vite-plus-linux-x64-musl@0.2.9':
+    resolution: {integrity: sha512-zuGx+eRotWPd9cmh1X9AfsC2tN/Ad9Hk6LAzlxoKJUjEkTsY3WjVJ6Da0z48SAUFuenI0JkdqXnMCrePtGvWHg==}
+    engines: {node: '>=20.0.0'}
+    cpu: [x64]
+    os: [linux]
+    libc: [musl]
+
+  '@voidzero-dev/vite-plus-test@0.1.24':
+    resolution: {integrity: sha512-9NiG6UadG0iOaPL1AMsO5sDKkx6MADHw4/mMOmHWZUhhUwqzfVtnnptMK37vD71e6KyR7yAscx19FrtOWWtjvA==}
+    engines: {node: ^20.0.0 || ^22.0.0 || >=24.0.0}
+    peerDependencies:
+      '@edge-runtime/vm': '*'
+      '@opentelemetry/api': ^1.9.0
+      '@types/node': ^25.6.0
+      '@vitest/coverage-istanbul': 4.1.8
+      '@vitest/coverage-v8': 4.1.8
+      '@vitest/ui': 4.1.8
+      happy-dom: '*'
+      jsdom: ^29.0.2
+      vite: ^6.0.0 || ^7.0.0 || ^8.0.0
+    peerDependenciesMeta:
+      '@edge-runtime/vm':
+        optional: true
+      '@opentelemetry/api':
+        optional: true
+      '@types/node':
+        optional: true
+      '@vitest/coverage-istanbul':
+        optional: true
+      '@vitest/coverage-v8':
+        optional: true
+      '@vitest/ui':
+        optional: true
+      happy-dom:
+        optional: true
+      jsdom:
+        optional: true
+
+  '@voidzero-dev/vite-plus-win32-arm64-msvc@0.1.24':
+    resolution: {integrity: sha512-G+/lhLKVjyn3FmgXX8jeWgq7RcE5O1kdR7QyFayQOdlMX/ZRkvUwQD7bFaqhKzgJM6Oj3a1FH3HQPYk5QOYuCQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
     cpu: [arm64]
-    os: [linux]
-    libc: [musl]
-
-  '@voidzero-dev/vite-plus-linux-x64-gnu@0.2.9':
-    resolution: {integrity: sha512-2Iy8x4PCPMNzXeu3pREevlggoeK8PwtdUiCpoSybAZBtR/aqMxsJREyt/eKv45F8lsiNlA8PbIWEvPxLSgzFLQ==}
-    engines: {node: '>=20.0.0'}
-    cpu: [x64]
-    os: [linux]
-    libc: [glibc]
-
-  '@voidzero-dev/vite-plus-linux-x64-musl@0.2.9':
-    resolution: {integrity: sha512-zuGx+eRotWPd9cmh1X9AfsC2tN/Ad9Hk6LAzlxoKJUjEkTsY3WjVJ6Da0z48SAUFuenI0JkdqXnMCrePtGvWHg==}
-    engines: {node: '>=20.0.0'}
-    cpu: [x64]
-    os: [linux]
-    libc: [musl]
+    os: [win32]
 
   '@voidzero-dev/vite-plus-win32-arm64-msvc@0.2.9':
     resolution: {integrity: sha512-kaKb5Q8ReYTBfvLgUhdpLJG3aoNF8HOVJpf8qBm+THsd4WRrkRwsBHp2ITsU8oXl2gnDjFGhPDaURegd/z6Wxw==}
@@ -11368,6 +11885,12 @@ packages:
     cpu: [arm64]
     os: [win32]
 
+  '@voidzero-dev/vite-plus-win32-x64-msvc@0.1.24':
+    resolution: {integrity: sha512-b0e5XohEV1w/RdzAtv8/Hm6tvHPXouPtBNsljjW/lDJZq3NCLND5s6lqe8H4IenrgmKSoqakHWtlqJqM36cFbw==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    cpu: [x64]
+    os: [win32]
+
   '@voidzero-dev/vite-plus-win32-x64-msvc@0.2.9':
     resolution: {integrity: sha512-/fEk3gbQTJknCiYM/GTL/L++Azsav8rCAjmtKrjmCbqEif5IMzqTfvM68n+PiLB3JVoQJGF/mg2niODr0IE/2w==}
     engines: {node: '>=20.0.0'}
@@ -12660,6 +13183,9 @@ packages:
     resolution: {integrity: sha512-Zf5H2Kxt2xjTvbJvP2ZWLEICxA6j+hAmMzIlypy4xcBg1vKVnx89Wy0GbS+kf5cwCVFFzdCFh2XSCFNULS6csw==}
     engines: {node: '>= 0.4'}
 
+  es-module-lexer@1.7.0:
+    resolution: {integrity: sha512-jEQoCwk8hyb2AZziIOLhDqpm5+2ww5uIE6lkO/6jcOCusfk6LhMHpXXfBLXTZ7Ydyt0j4VoUQv6uGNYbdW+kBA==}
+
   es-module-lexer@2.1.0:
     resolution: {integrity: sha512-n27zTYMjYu1aj4MjCWzSP7G9r75utsaoc8m61weK+W8JMBGGQybd43GstCXZ3WNmSFtGT9wi59qQTW6mhTR5LQ==}
 
@@ -14558,6 +15084,19 @@ packages:
     resolution: {integrity: sha512-qFOyK5PjiWZd+QQIh+1jhdb9LpxTF0qs7Pm8o5QHYZ0M3vKqSqzsZaEB6oWlxZ+q2sJBMI/Ktgd2N5ZwQoRHfg==}
     engines: {node: '>= 0.4'}
 
+  oxfmt@0.52.0:
+    resolution: {integrity: sha512-nJlYM35F64zTDMecCNhoHNkf+D/eHv7xcjj9XDSj+bFAVtN93m7v8DQMdHd6nDG6Akf/kEYYHmDUBs2Dz27Sug==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    hasBin: true
+    peerDependencies:
+      svelte: ^5.0.0
+      vite-plus: '*'
+    peerDependenciesMeta:
+      svelte:
+        optional: true
+      vite-plus:
+        optional: true
+
   oxfmt@0.62.0:
     resolution: {integrity: sha512-vxgGHTmnDU9j4CX7dDBLzxgmHxfda/yPcgJkGCMUSCwRmz+euo/V08xXLNgXTeqAB9Fhf3Pe2nO1RNKLCVgphQ==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -14571,10 +15110,27 @@ packages:
       vite-plus:
         optional: true
 
+  oxlint-tsgolint@0.23.0:
+    resolution: {integrity: sha512-3mBv3CoPbh8dFbzfDGIWa2ytZjn2v+3EX4aKRXjIhsoGFzG8GCjfRirz3rwZf1wYbZzsNLTSgpw8VjQuWdp/jA==}
+    hasBin: true
+
   oxlint-tsgolint@7.0.2001:
     resolution: {integrity: sha512-KjK/XLcXr1DSyonKhsuFqJRiuKqcyG9j3LJ8nkOsrLzGvodBPqzHOKauy10asLMDI0sUpvb+1sxlzff3udZvfg==}
     hasBin: true
 
+  oxlint@1.67.0:
+    resolution: {integrity: sha512-blwwaHPdoH8piQ5/z0KHeoHFR7FZgl12WluKJfu4qFLPkZl6mK04PkLE45Fw1NxfBRSlh40Gu7MkxHUw++ociQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    hasBin: true
+    peerDependencies:
+      oxlint-tsgolint: '>=0.22.1'
+      vite-plus: '*'
+    peerDependenciesMeta:
+      oxlint-tsgolint:
+        optional: true
+      vite-plus:
+        optional: true
+
   oxlint@1.77.0:
     resolution: {integrity: sha512-qnGh8XJHaQ0dprrDXNQZgS0FgjI6v+V3+X8DwmaV++5Aamy6jGKfDdQ1TUvhUxtmKFAbEf4/WeO5QZX+5WSngg==}
     engines: {node: ^20.19.0 || >=22.12.0}
@@ -14746,6 +15302,10 @@ packages:
     resolution: {integrity: sha512-QP88BAKvMam/3NxH6vj2o21R6MjxZUAd6nlwAS/pnGvN9IVLocLHxGYIzFhg6fUQ+5th6P4dv4eW9jX3DSIj7A==}
     engines: {node: '>=12'}
 
+  pixelmatch@7.2.0:
+    resolution: {integrity: sha512-xhcb4yHu9sM/G7foGzoLtXYcC0zHEaOXXjRKhGup0fw78Nf2Tkiapv4EQyMzrbcmQPsllAI7DbFY2UT7PlI9Pg==}
+    hasBin: true
+
   pkg-types@2.3.0:
     resolution: {integrity: sha512-SIqCzDRg0s9npO5XQ3tNZioRY1uK06lA41ynBC1YmFTmnY6FjUjVt6s4LoADmwoig1qqD0oK8h1p/8mlMx8Oig==}
 
@@ -16041,6 +16601,11 @@ packages:
       '@nuxt/kit':
         optional: true
 
+  vite-plus@0.1.24:
+    resolution: {integrity: sha512-b3fr6WtCiEhetjuzW/4KcEMOAMuZxoxZATWaXKmPzOLf1upG+pzKJOFZTb94D6wiPBlwcjxoaUtF7C3uAN+VjQ==}
+    engines: {node: ^20.19.0 || >=22.12.0}
+    hasBin: true
+
   vite-plus@0.2.9:
     resolution: {integrity: sha512-8uRNqAxh9no3AU4Lep8BEYhkim07+3NO+mhuxTWiN0k30syGT/2+ue/DtWYhtzQ7yi2f2WKpjOhoI4/QkWWbUg==}
     engines: {node: ^20.19.0 || ^22.18.0 || >=24.11.0}
@@ -18404,144 +18969,282 @@ snapshots:
 
   '@orama/orama@3.1.18': {}
 
+  '@oxc-project/runtime@0.133.0': {}
+
   '@oxc-project/runtime@0.143.0': {}
 
   '@oxc-project/types@0.124.0': {}
 
+  '@oxc-project/types@0.133.0': {}
+
   '@oxc-project/types@0.143.0': {}
 
+  '@oxfmt/binding-android-arm-eabi@0.52.0':
+    optional: true
+
   '@oxfmt/binding-android-arm-eabi@0.62.0':
     optional: true
 
+  '@oxfmt/binding-android-arm64@0.52.0':
+    optional: true
+
   '@oxfmt/binding-android-arm64@0.62.0':
     optional: true
 
+  '@oxfmt/binding-darwin-arm64@0.52.0':
+    optional: true
+
   '@oxfmt/binding-darwin-arm64@0.62.0':
     optional: true
 
+  '@oxfmt/binding-darwin-x64@0.52.0':
+    optional: true
+
   '@oxfmt/binding-darwin-x64@0.62.0':
     optional: true
 
+  '@oxfmt/binding-freebsd-x64@0.52.0':
+    optional: true
+
   '@oxfmt/binding-freebsd-x64@0.62.0':
     optional: true
 
+  '@oxfmt/binding-linux-arm-gnueabihf@0.52.0':
+    optional: true
+
   '@oxfmt/binding-linux-arm-gnueabihf@0.62.0':
     optional: true
 
+  '@oxfmt/binding-linux-arm-musleabihf@0.52.0':
+    optional: true
+
   '@oxfmt/binding-linux-arm-musleabihf@0.62.0':
     optional: true
 
+  '@oxfmt/binding-linux-arm64-gnu@0.52.0':
+    optional: true
+
   '@oxfmt/binding-linux-arm64-gnu@0.62.0':
     optional: true
 
+  '@oxfmt/binding-linux-arm64-musl@0.52.0':
+    optional: true
+
   '@oxfmt/binding-linux-arm64-musl@0.62.0':
     optional: true
 
+  '@oxfmt/binding-linux-ppc64-gnu@0.52.0':
+    optional: true
+
   '@oxfmt/binding-linux-ppc64-gnu@0.62.0':
     optional: true
 
+  '@oxfmt/binding-linux-riscv64-gnu@0.52.0':
+    optional: true
+
   '@oxfmt/binding-linux-riscv64-gnu@0.62.0':
     optional: true
 
+  '@oxfmt/binding-linux-riscv64-musl@0.52.0':
+    optional: true
+
   '@oxfmt/binding-linux-riscv64-musl@0.62.0':
     optional: true
 
+  '@oxfmt/binding-linux-s390x-gnu@0.52.0':
+    optional: true
+
   '@oxfmt/binding-linux-s390x-gnu@0.62.0':
     optional: true
 
+  '@oxfmt/binding-linux-x64-gnu@0.52.0':
+    optional: true
+
   '@oxfmt/binding-linux-x64-gnu@0.62.0':
     optional: true
 
+  '@oxfmt/binding-linux-x64-musl@0.52.0':
+    optional: true
+
   '@oxfmt/binding-linux-x64-musl@0.62.0':
     optional: true
 
+  '@oxfmt/binding-openharmony-arm64@0.52.0':
+    optional: true
+
   '@oxfmt/binding-openharmony-arm64@0.62.0':
     optional: true
 
+  '@oxfmt/binding-win32-arm64-msvc@0.52.0':
+    optional: true
+
   '@oxfmt/binding-win32-arm64-msvc@0.62.0':
     optional: true
 
+  '@oxfmt/binding-win32-ia32-msvc@0.52.0':
+    optional: true
+
   '@oxfmt/binding-win32-ia32-msvc@0.62.0':
     optional: true
 
+  '@oxfmt/binding-win32-x64-msvc@0.52.0':
+    optional: true
+
   '@oxfmt/binding-win32-x64-msvc@0.62.0':
     optional: true
 
+  '@oxlint-tsgolint/darwin-arm64@0.23.0':
+    optional: true
+
   '@oxlint-tsgolint/darwin-arm64@7.0.2001':
     optional: true
 
+  '@oxlint-tsgolint/darwin-x64@0.23.0':
+    optional: true
+
   '@oxlint-tsgolint/darwin-x64@7.0.2001':
     optional: true
 
+  '@oxlint-tsgolint/linux-arm64@0.23.0':
+    optional: true
+
   '@oxlint-tsgolint/linux-arm64@7.0.2001':
     optional: true
 
+  '@oxlint-tsgolint/linux-x64@0.23.0':
+    optional: true
+
   '@oxlint-tsgolint/linux-x64@7.0.2001':
     optional: true
 
+  '@oxlint-tsgolint/win32-arm64@0.23.0':
+    optional: true
+
   '@oxlint-tsgolint/win32-arm64@7.0.2001':
     optional: true
 
+  '@oxlint-tsgolint/win32-x64@0.23.0':
+    optional: true
+
   '@oxlint-tsgolint/win32-x64@7.0.2001':
     optional: true
 
+  '@oxlint/binding-android-arm-eabi@1.67.0':
+    optional: true
+
   '@oxlint/binding-android-arm-eabi@1.77.0':
     optional: true
 
+  '@oxlint/binding-android-arm64@1.67.0':
+    optional: true
+
   '@oxlint/binding-android-arm64@1.77.0':
     optional: true
 
+  '@oxlint/binding-darwin-arm64@1.67.0':
+    optional: true
+
   '@oxlint/binding-darwin-arm64@1.77.0':
     optional: true
 
+  '@oxlint/binding-darwin-x64@1.67.0':
+    optional: true
+
   '@oxlint/binding-darwin-x64@1.77.0':
     optional: true
 
+  '@oxlint/binding-freebsd-x64@1.67.0':
+    optional: true
+
   '@oxlint/binding-freebsd-x64@1.77.0':
     optional: true
 
+  '@oxlint/binding-linux-arm-gnueabihf@1.67.0':
+    optional: true
+
   '@oxlint/binding-linux-arm-gnueabihf@1.77.0':
     optional: true
 
+  '@oxlint/binding-linux-arm-musleabihf@1.67.0':
+    optional: true
+
   '@oxlint/binding-linux-arm-musleabihf@1.77.0':
     optional: true
 
+  '@oxlint/binding-linux-arm64-gnu@1.67.0':
+    optional: true
+
   '@oxlint/binding-linux-arm64-gnu@1.77.0':
     optional: true
 
+  '@oxlint/binding-linux-arm64-musl@1.67.0':
+    optional: true
+
   '@oxlint/binding-linux-arm64-musl@1.77.0':
     optional: true
 
+  '@oxlint/binding-linux-ppc64-gnu@1.67.0':
+    optional: true
+
   '@oxlint/binding-linux-ppc64-gnu@1.77.0':
     optional: true
 
+  '@oxlint/binding-linux-riscv64-gnu@1.67.0':
+    optional: true
+
   '@oxlint/binding-linux-riscv64-gnu@1.77.0':
     optional: true
 
+  '@oxlint/binding-linux-riscv64-musl@1.67.0':
+    optional: true
+
   '@oxlint/binding-linux-riscv64-musl@1.77.0':
     optional: true
 
+  '@oxlint/binding-linux-s390x-gnu@1.67.0':
+    optional: true
+
   '@oxlint/binding-linux-s390x-gnu@1.77.0':
     optional: true
 
+  '@oxlint/binding-linux-x64-gnu@1.67.0':
+    optional: true
+
   '@oxlint/binding-linux-x64-gnu@1.77.0':
     optional: true
 
+  '@oxlint/binding-linux-x64-musl@1.67.0':
+    optional: true
+
   '@oxlint/binding-linux-x64-musl@1.77.0':
     optional: true
 
+  '@oxlint/binding-openharmony-arm64@1.67.0':
+    optional: true
+
   '@oxlint/binding-openharmony-arm64@1.77.0':
     optional: true
 
+  '@oxlint/binding-win32-arm64-msvc@1.67.0':
+    optional: true
+
   '@oxlint/binding-win32-arm64-msvc@1.77.0':
     optional: true
 
+  '@oxlint/binding-win32-ia32-msvc@1.67.0':
+    optional: true
+
   '@oxlint/binding-win32-ia32-msvc@1.77.0':
     optional: true
 
+  '@oxlint/binding-win32-x64-msvc@1.67.0':
+    optional: true
+
   '@oxlint/binding-win32-x64-msvc@1.77.0':
     optional: true
 
+  '@oxlint/plugins@1.61.0': {}
+
   '@oxlint/plugins@1.73.0': {}
 
   '@pkgjs/parseargs@0.11.0':
@@ -21490,6 +22193,22 @@ snapshots:
       convert-source-map: 2.0.0
       tinyrainbow: 3.1.0
 
+  '@voidzero-dev/vite-plus-core@0.1.24(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(yaml@2.9.0)':
+    dependencies:
+      '@oxc-project/runtime': 0.133.0
+      '@oxc-project/types': 0.133.0
+      lightningcss: 1.33.0
+      postcss: 8.5.23
+    optionalDependencies:
+      '@types/node': 25.6.0
+      esbuild: 0.27.5
+      fsevents: 2.3.3
+      jiti: 2.6.1
+      terser: 5.46.2
+      tsx: 4.21.0
+      typescript: 5.9.3
+      yaml: 2.9.0
+
   '@voidzero-dev/vite-plus-core@0.2.9(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(typescript@7.0.2)(yaml@2.9.0)':
     dependencies:
       '@oxc-project/runtime': 0.143.0
@@ -21516,27 +22235,94 @@ snapshots:
       typescript: 7.0.2
       yaml: 2.9.0
 
+  '@voidzero-dev/vite-plus-darwin-arm64@0.1.24':
+    optional: true
+
   '@voidzero-dev/vite-plus-darwin-arm64@0.2.9':
     optional: true
 
+  '@voidzero-dev/vite-plus-darwin-x64@0.1.24':
+    optional: true
+
   '@voidzero-dev/vite-plus-darwin-x64@0.2.9':
     optional: true
 
+  '@voidzero-dev/vite-plus-linux-arm64-gnu@0.1.24':
+    optional: true
+
   '@voidzero-dev/vite-plus-linux-arm64-gnu@0.2.9':
     optional: true
 
+  '@voidzero-dev/vite-plus-linux-arm64-musl@0.1.24':
+    optional: true
+
   '@voidzero-dev/vite-plus-linux-arm64-musl@0.2.9':
     optional: true
 
+  '@voidzero-dev/vite-plus-linux-x64-gnu@0.1.24':
+    optional: true
+
   '@voidzero-dev/vite-plus-linux-x64-gnu@0.2.9':
     optional: true
 
+  '@voidzero-dev/vite-plus-linux-x64-musl@0.1.24':
+    optional: true
+
   '@voidzero-dev/vite-plus-linux-x64-musl@0.2.9':
     optional: true
 
+  '@voidzero-dev/vite-plus-test@0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(@vitest/ui@4.1.5)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(yaml@2.9.0)':
+    dependencies:
+      '@standard-schema/spec': 1.1.0
+      '@types/chai': 5.2.3
+      '@voidzero-dev/vite-plus-core': 0.1.24(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(yaml@2.9.0)
+      es-module-lexer: 1.7.0
+      obug: 2.1.1
+      pixelmatch: 7.2.0
+      pngjs: 7.0.0
+      sirv: 3.0.2
+      std-env: 4.0.0
+      tinybench: 2.9.0
+      tinyexec: 1.2.4
+      tinyglobby: 0.2.17
+      vite: 8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0)
+      ws: 8.20.0
+    optionalDependencies:
+      '@opentelemetry/api': 1.9.1
+      '@types/node': 25.6.0
+      '@vitest/ui': 4.1.5(vitest@4.1.10)
+      jsdom: 29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0)
+    transitivePeerDependencies:
+      - '@arethetypeswrong/core'
+      - '@tsdown/css'
+      - '@tsdown/exe'
+      - '@vitejs/devtools'
+      - bufferutil
+      - esbuild
+      - jiti
+      - less
+      - publint
+      - sass
+      - sass-embedded
+      - stylus
+      - sugarss
+      - terser
+      - tsx
+      - typescript
+      - unplugin-unused
+      - unrun
+      - utf-8-validate
+      - yaml
+
+  '@voidzero-dev/vite-plus-win32-arm64-msvc@0.1.24':
+    optional: true
+
   '@voidzero-dev/vite-plus-win32-arm64-msvc@0.2.9':
     optional: true
 
+  '@voidzero-dev/vite-plus-win32-x64-msvc@0.1.24':
+    optional: true
+
   '@voidzero-dev/vite-plus-win32-x64-msvc@0.2.9':
     optional: true
 
@@ -22870,6 +23656,8 @@ snapshots:
 
   es-errors@1.3.0: {}
 
+  es-module-lexer@1.7.0: {}
+
   es-module-lexer@2.1.0: {}
 
   es-object-atoms@1.1.1:
@@ -25077,6 +25865,31 @@ snapshots:
       object-keys: 1.1.1
       safe-push-apply: 1.0.0
 
+  oxfmt@0.52.0(vite-plus@0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(vitest@4.1.10)(yaml@2.9.0)):
+    dependencies:
+      tinypool: 2.1.0
+    optionalDependencies:
+      '@oxfmt/binding-android-arm-eabi': 0.52.0
+      '@oxfmt/binding-android-arm64': 0.52.0
+      '@oxfmt/binding-darwin-arm64': 0.52.0
+      '@oxfmt/binding-darwin-x64': 0.52.0
+      '@oxfmt/binding-freebsd-x64': 0.52.0
+      '@oxfmt/binding-linux-arm-gnueabihf': 0.52.0
+      '@oxfmt/binding-linux-arm-musleabihf': 0.52.0
+      '@oxfmt/binding-linux-arm64-gnu': 0.52.0
+      '@oxfmt/binding-linux-arm64-musl': 0.52.0
+      '@oxfmt/binding-linux-ppc64-gnu': 0.52.0
+      '@oxfmt/binding-linux-riscv64-gnu': 0.52.0
+      '@oxfmt/binding-linux-riscv64-musl': 0.52.0
+      '@oxfmt/binding-linux-s390x-gnu': 0.52.0
+      '@oxfmt/binding-linux-x64-gnu': 0.52.0
+      '@oxfmt/binding-linux-x64-musl': 0.52.0
+      '@oxfmt/binding-openharmony-arm64': 0.52.0
+      '@oxfmt/binding-win32-arm64-msvc': 0.52.0
+      '@oxfmt/binding-win32-ia32-msvc': 0.52.0
+      '@oxfmt/binding-win32-x64-msvc': 0.52.0
+      vite-plus: 0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(vitest@4.1.10)(yaml@2.9.0)
+
   oxfmt@0.62.0(vite-plus@0.2.9(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(@vitest/browser-playwright@4.1.10)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(msw@2.11.5(@types/node@25.6.0)(typescript@7.0.2))(terser@5.46.2)(tsx@4.21.0)(typescript@7.0.2)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(yaml@2.9.0)):
     dependencies:
       tinypool: 2.1.0
@@ -25102,6 +25915,15 @@ snapshots:
       '@oxfmt/binding-win32-x64-msvc': 0.62.0
       vite-plus: 0.2.9(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(@vitest/browser-playwright@4.1.10)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(msw@2.11.5(@types/node@25.6.0)(typescript@7.0.2))(terser@5.46.2)(tsx@4.21.0)(typescript@7.0.2)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(yaml@2.9.0)
 
+  oxlint-tsgolint@0.23.0:
+    optionalDependencies:
+      '@oxlint-tsgolint/darwin-arm64': 0.23.0
+      '@oxlint-tsgolint/darwin-x64': 0.23.0
+      '@oxlint-tsgolint/linux-arm64': 0.23.0
+      '@oxlint-tsgolint/linux-x64': 0.23.0
+      '@oxlint-tsgolint/win32-arm64': 0.23.0
+      '@oxlint-tsgolint/win32-x64': 0.23.0
+
   oxlint-tsgolint@7.0.2001:
     optionalDependencies:
       '@oxlint-tsgolint/darwin-arm64': 7.0.2001
@@ -25111,6 +25933,30 @@ snapshots:
       '@oxlint-tsgolint/win32-arm64': 7.0.2001
       '@oxlint-tsgolint/win32-x64': 7.0.2001
 
+  oxlint@1.67.0(oxlint-tsgolint@0.23.0)(vite-plus@0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(vitest@4.1.10)(yaml@2.9.0)):
+    optionalDependencies:
+      '@oxlint/binding-android-arm-eabi': 1.67.0
+      '@oxlint/binding-android-arm64': 1.67.0
+      '@oxlint/binding-darwin-arm64': 1.67.0
+      '@oxlint/binding-darwin-x64': 1.67.0
+      '@oxlint/binding-freebsd-x64': 1.67.0
+      '@oxlint/binding-linux-arm-gnueabihf': 1.67.0
+      '@oxlint/binding-linux-arm-musleabihf': 1.67.0
+      '@oxlint/binding-linux-arm64-gnu': 1.67.0
+      '@oxlint/binding-linux-arm64-musl': 1.67.0
+      '@oxlint/binding-linux-ppc64-gnu': 1.67.0
+      '@oxlint/binding-linux-riscv64-gnu': 1.67.0
+      '@oxlint/binding-linux-riscv64-musl': 1.67.0
+      '@oxlint/binding-linux-s390x-gnu': 1.67.0
+      '@oxlint/binding-linux-x64-gnu': 1.67.0
+      '@oxlint/binding-linux-x64-musl': 1.67.0
+      '@oxlint/binding-openharmony-arm64': 1.67.0
+      '@oxlint/binding-win32-arm64-msvc': 1.67.0
+      '@oxlint/binding-win32-ia32-msvc': 1.67.0
+      '@oxlint/binding-win32-x64-msvc': 1.67.0
+      oxlint-tsgolint: 0.23.0
+      vite-plus: 0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(vitest@4.1.10)(yaml@2.9.0)
+
   oxlint@1.77.0(oxlint-tsgolint@7.0.2001)(vite-plus@0.2.9(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(@vitest/browser-playwright@4.1.10)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(msw@2.11.5(@types/node@25.6.0)(typescript@7.0.2))(terser@5.46.2)(tsx@4.21.0)(typescript@7.0.2)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(yaml@2.9.0)):
     optionalDependencies:
       '@oxlint/binding-android-arm-eabi': 1.77.0
@@ -25283,6 +26129,10 @@ snapshots:
 
   picomatch@4.0.4: {}
 
+  pixelmatch@7.2.0:
+    dependencies:
+      pngjs: 7.0.0
+
   pkg-types@2.3.0:
     dependencies:
       confbox: 0.2.4
@@ -26891,6 +27741,57 @@ snapshots:
       - typescript
       - ws
 
+  vite-plus@0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(vitest@4.1.10)(yaml@2.9.0):
+    dependencies:
+      '@oxc-project/types': 0.133.0
+      '@oxlint/plugins': 1.61.0
+      '@vitest/ui': 4.1.5(vitest@4.1.10)
+      '@voidzero-dev/vite-plus-core': 0.1.24(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(yaml@2.9.0)
+      '@voidzero-dev/vite-plus-test': 0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(@vitest/ui@4.1.5)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(yaml@2.9.0)
+      oxfmt: 0.52.0(vite-plus@0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(vitest@4.1.10)(yaml@2.9.0))
+      oxlint: 1.67.0(oxlint-tsgolint@0.23.0)(vite-plus@0.1.24(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(terser@5.46.2)(tsx@4.21.0)(typescript@5.9.3)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(vitest@4.1.10)(yaml@2.9.0))
+      oxlint-tsgolint: 0.23.0
+    optionalDependencies:
+      '@voidzero-dev/vite-plus-darwin-arm64': 0.1.24
+      '@voidzero-dev/vite-plus-darwin-x64': 0.1.24
+      '@voidzero-dev/vite-plus-linux-arm64-gnu': 0.1.24
+      '@voidzero-dev/vite-plus-linux-arm64-musl': 0.1.24
+      '@voidzero-dev/vite-plus-linux-x64-gnu': 0.1.24
+      '@voidzero-dev/vite-plus-linux-x64-musl': 0.1.24
+      '@voidzero-dev/vite-plus-win32-arm64-msvc': 0.1.24
+      '@voidzero-dev/vite-plus-win32-x64-msvc': 0.1.24
+    transitivePeerDependencies:
+      - '@arethetypeswrong/core'
+      - '@edge-runtime/vm'
+      - '@opentelemetry/api'
+      - '@tsdown/css'
+      - '@tsdown/exe'
+      - '@types/node'
+      - '@vitejs/devtools'
+      - '@vitest/coverage-istanbul'
+      - '@vitest/coverage-v8'
+      - bufferutil
+      - esbuild
+      - happy-dom
+      - jiti
+      - jsdom
+      - less
+      - publint
+      - sass
+      - sass-embedded
+      - stylus
+      - sugarss
+      - svelte
+      - terser
+      - tsx
+      - typescript
+      - unplugin-unused
+      - unrun
+      - utf-8-validate
+      - vite
+      - vitest
+      - yaml
+
   vite-plus@0.2.9(@opentelemetry/api@1.9.1)(@types/node@25.6.0)(@vitest/browser-playwright@4.1.10)(esbuild@0.27.5)(jiti@2.6.1)(jsdom@29.0.2(@noble/hashes@2.0.1)(canvas@3.1.0))(msw@2.11.5(@types/node@25.6.0)(typescript@7.0.2))(terser@5.46.2)(tsx@4.21.0)(typescript@7.0.2)(vite@8.0.8(@types/node@25.6.0)(esbuild@0.27.5)(jiti@2.6.1)(terser@5.46.2)(tsx@4.21.0)(yaml@2.9.0))(yaml@2.9.0):
     dependencies:
       '@oxc-project/types': 0.143.0
diff --git a/tests/src/end-to-end/multicolumn/multicolumn.test.tsx b/tests/src/end-to-end/multicolumn/multicolumn.test.tsx
index 77cd1cd21d..063ebb68cd 100644
--- a/tests/src/end-to-end/multicolumn/multicolumn.test.tsx
+++ b/tests/src/end-to-end/multicolumn/multicolumn.test.tsx
@@ -11,6 +11,7 @@ import {
 import {
   compareDocToSnapshot,
   focusOnEditor,
+  sleep,
   waitForSelector,
 } from "../../utils/editor.js";
 import {
@@ -134,3 +135,59 @@ describe("Check Multi-Column Behaviour", () => {
     await compareDocToSnapshot("deleteEndOfColumnList");
   });
 });
+
+// Which block the side menu attaches to is resolved from live layout
+// (`elementsFromPoint` / `posAtCoords`). The pieces below that are covered
+// closer to the code: the arithmetic in
+// `packages/core/src/extensions/SideMenu/sideMenuContainerGeometry.test.ts`
+// (node, plain rects) and the DOM/layout adapters in the `.browser.test.ts`
+// beside it. This is the whole path, through a real column list.
+//
+// Each column carries 25px of its own left padding and the side menu renders
+// into it, so the coordinates the lookup is handed belong to one column while
+// horizontally overlapping the column before it. `SideMenu.ts` compensates by
+// re-probing 50px further right once `isHorizontalContainer` recognises the
+// column list; drop that (or let the detection fail — a `display: contents`
+// element reports a zero rect, which is exactly what would silently defeat it)
+// and the menu attaches to a block in the *previous* column instead. Only the
+// padding is affected: hovering a block's own text resolves correctly either
+// way, which is why this can't be tested by hovering a block.
+describe("Check side menu placement inside a column list", () => {
+  /** Vertical centre of a rect — what the menu lines itself up with. */
+  const centerY = (rect: DOMRect) => rect.y + rect.height / 2;
+
+  test("Check drag handle resolves the block on the hovered row of a column", async () => {
+    await focusOnEditor();
+
+    // The last column is the only one holding several blocks, so it's the only
+    // place a wrongly resolved block is distinguishable by its row.
+    const target = page.getByText("Block 2").element();
+    const columnRect = getRect(target.closest(".bn-block-column")!);
+
+    await mouseSequence([
+      {
+        type: "move",
+        x: columnRect.x + 5,
+        y: centerY(getRect(target)),
+        steps: 5,
+      },
+    ]);
+    await waitForSelector(DRAG_HANDLE_SELECTOR);
+    await sleep(150);
+    const handleRect = getRect(DRAG_HANDLE_SELECTOR);
+
+    expect(handleRect.x).toBeLessThan(getRect(target).x);
+
+    // The handle lines up with the hovered block's row rather than any other
+    // block's — a stronger claim than a pixel tolerance would be, since every
+    // candidate is only a line-height away, and it's what distinguishes this
+    // column's blocks from the neighbouring column's.
+    const distance = (rect: DOMRect) =>
+      Math.abs(centerY(handleRect) - centerY(rect));
+    for (const other of ["Block 1", "Block 3", "So is this heading!"]) {
+      expect(distance(getRect(target))).toBeLessThan(
+        distance(getRect(page.getByText(other).element())),
+      );
+    }
+  });
+});
diff --git a/tests/src/end-to-end/y-prosemirror/fixtures/suggestionFixture.tsx b/tests/src/end-to-end/y-prosemirror/fixtures/suggestionFixture.tsx
index f3e12560d9..2c768cff6c 100644
--- a/tests/src/end-to-end/y-prosemirror/fixtures/suggestionFixture.tsx
+++ b/tests/src/end-to-end/y-prosemirror/fixtures/suggestionFixture.tsx
@@ -348,8 +348,8 @@ function opToXml(op: DeltaInsertOp): string {
   // concurrent merge of two marks), which would otherwise make these
   // snapshots flaky. Sorted ascending => the alphabetically-first mark
   // ends up innermost (e.g. `<italic><bold>world</bold></italic>`).
-  for (const [name, value] of Object.entries(op.format ?? {}).sort(([a], [b]) =>
-    a < b ? -1 : a > b ? 1 : 0,
+  for (const [name, value] of Object.entries(op.format ?? {}).sort(
+    ([a], [b]) => (a < b ? -1 : a > b ? 1 : 0),
   )) {
     if (value !== null && typeof value === "object") {
       // Object value: trivial empty `{}` renders as a bare tag, richer
diff --git a/tests/src/unit/react/useNodeViewBlock.test.tsx b/tests/src/unit/react/useNodeViewBlock.test.tsx
index 71101c7fa7..9f265e5380 100644
--- a/tests/src/unit/react/useNodeViewBlock.test.tsx
+++ b/tests/src/unit/react/useNodeViewBlock.test.tsx
@@ -27,8 +27,15 @@ const createReproBlock = createReactBlockSpec(
   { render: (props) => <p ref={props.contentRef} /> },
 );
 
+// A container block, whose node view's node IS the bnBlock — resolved by id
+// instead of by position.
+const createBoxBlock = createReactBlockSpec(
+  { type: "box", propSchema: {}, content: "none", children: {} },
+  { render: (props) => <div ref={props.contentRef} /> },
+);
+
 const schema = BlockNoteSchema.create().extend({
-  blockSpecs: { repro: createReproBlock() },
+  blockSpecs: { repro: createReproBlock(), box: createBoxBlock() },
 });
 
 let editor: BlockNoteEditor<any, any, any>;
@@ -43,6 +50,7 @@ beforeEach(() => {
       { type: "paragraph", content: "first" },
       { type: "repro", content: "target block" },
       { type: "paragraph", content: "last" },
+      { type: "box", children: [{ type: "paragraph", content: "inside" }] },
     ],
   }) as BlockNoteEditor<any, any, any>;
 
@@ -78,11 +86,14 @@ function renderHook(
   return resolved;
 }
 
-// Only the two fields `useNodeViewBlock` reads. Built structurally so `tests`
-// doesn't need a dependency on `@tiptap/react` just for its prop types.
-function makeProps(getPos: () => number | undefined) {
+// Only the fields `useNodeViewBlock` reads. Built structurally so `tests`
+// doesn't need a dependency on `@tiptap/react` just for its prop types. The
+// `node` defaults to a regular (non-container) block's node shape; container
+// tests pass the real PM node instead.
+function makeProps(getPos: () => number | undefined, node?: unknown) {
   return {
     getPos,
+    node: node ?? { type: { isInGroup: () => false } },
     view: { state: { doc: editor.prosemirrorState.doc } },
   } as unknown as Parameters<typeof useNodeViewBlock>[0];
 }
@@ -170,4 +181,34 @@ describe("useNodeViewBlock", () => {
     expect(resolved.id).toBe(target.id);
     expect(resolved).not.toBe(seed);
   });
+
+  it("rejects container blocks loudly instead of resolving the wrong block", () => {
+    const box = editor.document[3];
+    const { node } = getNodeById(box.id, editor.prosemirrorState.doc)!;
+    const props = makeProps(() => undefined, node);
+
+    let captured: unknown;
+
+    function Probe() {
+      useNodeViewBlock(props, box);
+      return null;
+    }
+
+    root = createRoot(div, {
+      // React 19 reports uncaught render errors here instead of rethrowing
+      // out of `flushSync`.
+      onUncaughtError: (error: unknown) => {
+        captured = error;
+      },
+    });
+    try {
+      flushSync(() => {
+        root!.render(<Probe />);
+      });
+    } catch (error) {
+      captured = error;
+    }
+
+    expect(String(captured)).toMatch(/cannot resolve container block "box"/);
+  });
 });