Intent to Ship: Popover=hint "new behaviours"

[Keith Cirkel]

Summary: `popover=hint` attribute changed behaviours to smooth over some edge cases 

Bug: https://bugzilla.mozilla.org/show_bug.cgi?id=2029974

Specification: https://html.spec.whatwg.org/#attr-popover-hint-state

Standards Body: WHATWG

Platform coverage: All

Preference: N/A

Devtools bug: N/A

Other browsers:

  - Blink: Shipping original behaviour in M133, new behaviour in M150.

  - WebKit: Positive (https://github.com/WebKit/standards-positions/issues/305).

web-platform-tests: Extensive WPTs, for e.g. https://wpt.fyi/results/html/semantics/popovers/popover-light-dismiss-hint.html https://wpt.fyi/results/html/semantics/popovers/popover-top-layer-nesting-hints.html

popover=hint was proposed as a focus area for Interop 2026 (https://github.com/web-platform-tests/interop/issues/1129). We shipped support for this in 149. Over the past few months we (predominantly Jake Archibald) have been discovering several edge cases which has let to some work to redefine the behaviours for this feature. I've been working alongside, refactoring per the spec changes, in https://phabricator.services.mozilla.com/D292397.

Blink have been landing their changes around this, including WPTs. This has caused us to regress our Interop 2026 score from 100% to 93.1%. We acknowledge and anticipated this. Landing D292397 should bring us back to 100% (modulo also landing https://github.com/web-platform-tests/wpt/pull/59955).

I intend to land this shortly (today or tomorrow). This new behaviour will therefore likely land in 153, after riding the nightly trains for a full cycle. We do not anticipate any issues, the behaviour changes make this feature more useful and understandable, nevertheless if we encounter issues we have plenty of time to discover & adapt or roll back.

If anyone has any concerns please let me know!

Happy browsing.