Add popover=hint

[josepharhar]

Fixes #9776

Explainer: https://open-ui.org/components/popover-hint.research.explainer/#popoverhint-behavior

• At least two implementers are interested (and none opposed):
  • Chrome
  • popover=hint WebKit/standards-positions#305
  • popover=hint mozilla/standards-positions#965
• Tests are written and can be reviewed and commented upon at:
  • https://wpt.fyi/results/html/semantics/popovers/popover-types-with-hints.tentative.html
• Implementation bugs are filed:
  • Chromium: Implemented
  • Gecko: …
  • WebKit: …
• MDN issue is filed: …

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

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/interactive-elements.html ( diff )
/popover.html ( diff )

[nt1m]

I would probably want https://github.com/keithamus/invoker-buttons-proposal to be worked on first before addressing this, as I think it's a building block for this and other declarative attributes.

[mfreed7]

I would probably want https://github.com/keithamus/invoker-buttons-proposal to be worked on first before addressing this, as I think it's a building block for this and other declarative attributes.

So I've significantly updated the popover=hint explainer, and there are a few sections detailing why I believe the functionality described in this PR is independent of the hover-triggering functionality described by the Invokers explainer (note that it was moved to the OpenUI repo). See this section:

• https://open-ui.org/components/popover-hint.research.explainer/#tooltip-lifecycle-behaviors

Indeed both are important bits of functionality, but I'm hoping we can tackle them independently rather than needing to put up another huge spec PR. That didn't work very well for the original Popover spec PR, at least in my opinion.

[josepharhar]

Note to self: this will require additional changes in https://chromium-review.googlesource.com/c/chromium/src/+/5229300 if the corresponding PR to be opened gets merged

[mfreed7]

Ok, I reviewed mostly for the correctness of the algorithms, and things look pretty good. I made a few corrections, but other than those, LGTM.

[mfreed7]

Gentle ping - any chance we could get an initial review of this PR? @annevk @domenic

[domenic]

A few more editorial nits

[domenic]

LGTM with final nit