[html-aam] Set heading level based on HTML computed heading level

[keithamus]

Refs whatwg/html#11086.

This wires up HTML-AAM to the headingoffset feature of the html spec which defines an algorithm for computing a heading level.

Test, Documentation and Implementation tracking

Once this PR has been reviewed and has consensus from the working group, tests should be written and issues should be opened on browsers. Add N/A and check when not applicable.

• "author MUST" tests:
• "user agent MUST" tests:
• Browser implementations (link to issue or commit):
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=295092
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=1974383
  • Blink: https://issues.chromium.org/issues/333628468
• ACT review?
• Does this need AT implementations?
• Related APG Issue/PR:
• MDN Issue/PR:

[netlify]

✅ Deploy Preview for wai-aria ready!

Name	Link
🔨 Latest commit	d8cbe85
🔍 Latest deploy log	https://app.netlify.com/projects/wai-aria/deploys/697113dc65608300085a436d
😎 Deploy Preview	https://deploy-preview-2598--wai-aria.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[rahimabdi]

Should the WebKit bug link to: https://bugs.webkit.org/show_bug.cgi?id=295092?

[scottaohara]

can't make the meeting today, so wanted to get in a quick review. thank you again for working on this.

[scottaohara]

initial reaction to this is "awesome! this is moving forward!"

But, in regards to how these new features should be specified in this spec, it might be best to combine the proposed updated text with the original text. e.g., indicate that the default level of a heading element would correlate to the number used in the tag name. But, the computed heading level of the element can be adjusted if also used with the new headingoffset and headingreset attributes.

Then those attributes would need to be added to the attributes table (so then their mention in the heading element mapping table can then in-doc link to those attributes) indicating how they can adjust the heading level (aria-level) mapping for in-scope heading elements.

Probably also worth adding a note stating that specifying an aria-level attribute will take priority over whatever the implicit aria-level would be exposed as.

[Copilot]

Pull Request Overview

This PR updates the HTML-AAM specification to use the HTML computed heading level algorithm instead of simply using the number in the heading element's tag name for setting the aria-level property. This change aligns with recent HTML specification updates that introduce a headingoffset feature for computing heading levels.

Key changes:

• Updates the mapping for h1-h6 elements to reference the HTML spec's computed heading level algorithm
• Replaces direct tag name number usage with a more sophisticated heading level calculation

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.
You can also share your feedback on Copilot code review for a chance to win a $100 gift card. Take the survey.}

[Copilot]

There is an extra "the" in the phrase "set to the the computed heading level". It should be "set to the computed heading level".

Suggested change

	<a class="core-mapping" href="#role-map-heading">`heading`</a> role, with the <a class="core-mapping" href="#ariaLevel">`aria-level`</a> property set to the <a data-cite="html/sections.html#get-an-element's-computed-heading-offset">the computed heading level</a>.
	<a class="core-mapping" href="#role-map-heading">`heading`</a> role, with the <a class="core-mapping" href="#ariaLevel">`aria-level`</a> property set to <a data-cite="html/sections.html#get-an-element's-computed-heading-offset">the computed heading level</a>.

[pkra]

The upstream PR has landed. Should this move out of draft, @keithamus ?

[keithamus]

Closing this in favour of #2720 which is both updated but also pushed to the right remote, so that we get deploy previews.