Ensure modal dialogs can nest inside of hint popovers

[keithamus]

This change allows for dialogs that are nested inside of a hint popover to be shown as modal. The current spec, as written, means that dialogs may close their parent hint popover causing issues similar to #9998. This change makes it such that a dialog (or fullscreen element) is a viable candidate to nest inside of a hint popover.

This behaviour is exhibited in all major engines (which currently allow modal dialogs to nest inside of hint popovers) including Chrome, making this change normative.

This closes #11008, by making the spec modifications @Gingeh suggests in that issue.

• At least two implementers are interested (and none opposed):
  • Chromium: Already exhibits this behaviour (see Hint popovers can't be the "topmost open popover ancestor" of dialog elements #11008
  • Ladybird: Interested.
  • Gecko: Interested.
• Tests are written and can be reviewed and commented upon at:
  • https://wpt.live/html/semantics/popovers/popover-top-layer-nesting-hints.html
• Implementation bugs are filed:
  • Chromium: N/A, Chrome already allows nesting.
  • Gecko: N/A, Gecko already allows this kind of nesting.
  • WebKit: N/A, WebKit already allows this kind of nesting.
  • Deno (only for timers, structured clone, base64 utils, channel messaging, module resolution, web workers, and web storage): …
  • Node.js (only for timers, structured clone, base64 utils, channel messaging, and module resolution): …
• Corresponding HTML AAM & ARIA in HTML issues & PRs: N/A not an a11y issue.
• MDN issue is filed: N/A this is effectively normative, I don't think docs need to be changed here.
• The top of this comment includes a clear commit message to use.

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

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/popover.html ( diff )

[keithamus]

/cc @mfreed7 @josepharhar @nt1m

[mfreed7]

LGTM, thanks for putting this up!

[Gingeh]

Thanks for this!
"nearest inclusive open popover" also needs to be updated to allow hint popovers to complete the fix

[domenic]

Editorially LGTM, but can you fill out the checkboxes?

[keithamus]

@annevk or @nt1m can I get WebKit's support of this change?

[annevk]

If the specification is out of line with multiple implementations and the implementations are aligned, there's generally no need to seek implementer interest. (Also, in this case you had interest from Chromium and presumably you could have given interest from Gecko.) (But also, it's fine to ask regardless. I thought to share this in case it's useful in the future.)

You do need to fix the duplicate "or".

[annevk]

Oh, this is not the case I thought it was as Gecko and WebKit do not support popover=hint. I guess the test doesn't fail early if that's not supported? (Perhaps it could be considered a bug fix for the popover=hint PR, but that's not entirely clear.)

In that case I'm going to defer to @nt1m for WebKit, but this is probably fine.

[Gingeh]

Could Ladybird count as an "interested implementer" for this?

[keithamus]

Just rebased this to remove the conflicts, so this should be good to merge now.