Bug 235400 - Implement at-rule function for use with @supports
Summary: Implement at-rule function for use with @supports
Status: NEW
Alias: None
Product: WebKit
Classification: Unclassified
Component: CSS (show other bugs)
Version: WebKit Nightly Build
Hardware: Unspecified Unspecified
: P2 Normal
Assignee: Nobody
Keywords: InRadar
Depends on:
Reported: 2022-01-20 05:31 PST by Bramus
Modified: 2023-05-01 14:41 PDT (History)
3 users (show)

See Also:


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Description Bramus 2022-01-20 05:31:03 PST
As per CSS WG Decision [1]: Implement at-rule function for use with @supports


/* Just the at-rule name, which returns whether this is a recognized at-rule name at all. */
@supports(at-rule(@foo)) {
  /* @foo is supported */

/* An at-rule name accompanied by a descriptor declaration, which returns whether the at-rule is recognized, and the given descriptor successfully parses as part of that at-rule.*/
@supports(at-rule(@foo; desc: val)) {
  /* @foo with the descriptor `desc` and value `val` is supported */

Note that there's a follow-up issue [2] to extend at-rule() with a third syntax which allows passing in an entire at-rule into at-rule().

/* An entire at-rule, which returns whether or not the at-rule as a whole, when parsed as the first and only content in a fresh stylesheet, is valid or dropped. If the at-rule is valid but drops some of its contents as invalid, such as an unknown descriptor, this will still return true. */
@supports(at-rule(@foo bar {baz: qux})) {
  /* The entire at-rule is supported */

It also supports 
At the moment, this third syntax is still a WIP.

^[1] https://github.com/w3c/csswg-drafts/issues/2463#issuecomment-1016720310
^[2] https://github.com/w3c/csswg-drafts/issues/6966
Comment 1 Radar WebKit Bug Importer 2022-01-21 08:24:55 PST