Review request before CR: CSS `selector()`

[svgeesus]

Braw mornin' TAG!

I'm requesting a TAG review of CSS selector().

CSS @supports enables conditional application of style based on support for properties and property values; this specification adds the missing piece, checking for support of selectors.

• Explainer¹ (minimally containing user needs and example code): https://github.com/dbaron/css-supports-functions/blob/main/explainer.md
• Specification URL: https://www.w3.org/TR/css-conditional-4/
• Tests: [wpt folder(s), if available]
  • https://wpt.fyi/results/css/css-conditional?label=experimental&label=master&aligned
  • https://github.com/web-platform-tests/wpt/tree/master/css/css-conditional
  • inline in specification
• User research: From explainer "Having feature queries based on selectors is probably the highest priority addition".
• Security and Privacy self-review²: https://www.w3.org/TR/css-conditional-4/#privacy https://www.w3.org/TR/css-conditional-4/#security
• GitHub repo (if you prefer feedback filed there): CSSWG repo
• Primary contacts (and their relationship to the specification):
  • L. David Baron ( @dbaron ), Invited Expert: editor
  • Elika J. Etemad / fantasai ( @fantasai ), Invited Expert: editor
  • Chris Lilley ( @svgeesus ), W3C: editor
• Organization(s)/project(s) driving the specification: all browsers
• Key pieces of existing multi-stakeholder review or discussion of this specification: Closed CSS issue #3207
• External status/issue trackers for this specification (publicly visible, e.g. Chrome Status): already implemented, so no open bug trackers

Further details:

• [x] I have reviewed the TAG's Web Platform Design Principles
• Relevant time constraints or deadlines: We are hoping to move this small specification to CR very soon
• The group where the work on this specification is currently being done: CSSWG
• The group where standardization of this work is intended to be done (if current group is a community group or other incubation venue): CSSWG
• Major unresolved issues with or opposition to this specification: None
• This work is being funded by: n/a

You should also know that...

• selector() is the only new feature in CSS Conditional 4, compared to CSS Conditional 3
• MDN article on checking for supported selectors
• CanIUse shows support in all browsers
• wide review for the previous level, CSS Conditional 3, which is now implemented everywhere
• Wide review meta-issue for CSS Conditional 4

We'd prefer the TAG provide feedback as (please delete all but the desired option):

🐛 open issues in our GitHub repo for each point of feedback

[LeaVerou]

We looked at this during a breakout today. We don't see any issues with this feature and are happy for it to move forward.

[kirav]

not sure if anyone will look here, but

@supports not (selector(::-webkit-scrollbar)) {
    scrollbar-color: var(--primary) #fff;
    scrollbar-width: thin;
  }

this code does not compile properly @supports not (selector(::-webkit-scrollbar)) TERM IS EXPECTED :(