Add name attribute for grouping details elements into an exclusive accordion

[dbaron]

This PR adds a name attribute to the details element. This has been discussed a bit in the Open UI Community Group and I've written an explainer for it.

This work began as part of the followup work after pausing work on CSS Toggles. For some recent discussions in the Open UI Comunity Group, see May 25 minutes and June 1 minutes for recent discussions.

• At least two implementers are interested (and none opposed):
  • Chromium (see prototyping work in https://crbug.com/1444057)
  • Mozilla (see Exclusive accordions with <details name=""> mozilla/standards-positions#831)
  • WebKit (see exclusive accordions with <details name=""> WebKit/standards-positions#209)
• Tests are written and can be reviewed and commented upon at:
  • https://wpt.fyi/results/html/semantics/interactive-elements/the-details-element/name-attribute.tentative.html (created in Implement prototype of name attribute for details element. web-platform-tests/wpt#39925 and Allow newly-added test to also pass when mutation events are not fired. web-platform-tests/wpt#40065)
• Implementation bugs are filed:
  • Chromium: https://crbug.com/1444057
  • Gecko: https://bugzilla.mozilla.org/show_bug.cgi?id=1856460
  • WebKit: https://bugs.webkit.org/show_bug.cgi?id=260893
• MDN issue is filed: …

(See WHATWG Working Mode: Changes for more details.)

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/dom.html ( diff )
/dynamic-markup-insertion.html ( diff )
/indices.html ( diff )
/interactive-elements.html ( diff )