Intent to prototype and ship: <hr> in <select>

[Oliver Medhurst]

As of today (Firefox 122), I intend to turn on <hr> in <select> by default on all platforms. It has not been developed behind a flag as it is a low-risk feature and we pass web platform tests. Blink and WebKit already ship it at this time.

Summary:

Allowing <hr> in <select> lets websites use separators in a <select> menu with a simple <hr> element, instead of having to use a disabled option which is blank, "------", etc.

While we do support this feature completely on desktop, currently on Android separators are not rendered so will not appear in menus, but it is not blocking shipping this feature generally. See https://bugzil.la/1867045

Bug: https://bugzil.la/1830909
Specification: https://html.spec.whatwg.org/#the-hr-element
Standards body: WHATWG (HTML)
Platform coverage: All

Preference: None
DevTools bug: None
Standards position: https://github.com/mozilla/standards-positions/issues/887

Other browsers:
- Blink: Shipped since Chrome 119
- WebKit: Shipped since Safari 17

Web platform tests: https://wpt.fyi/results/html/syntax/parsing?q=html5lib_webkit02 (parsing only)