235400 2022-01-20 05:31:03 -0800 Implement at-rule function for use with @supports 2024-07-15 21:37:32 -0700 1 1 1 Unclassified WebKit CSS WebKit Nightly Build Unspecified Unspecified NEW InRadar P2 Normal --- 1 bramus webkit-unassigned ik koivisto ryan sebastianzartner webkit-bug-importer oldest_to_newest 1832401 0 bramus 2022-01-20 05:31:03 -0800 As per CSS WG Decision [1]: Implement at-rule function for use with @supports Syntax: ```css /* Just the at-rule name, which returns whether this is a recognized at-rule name at all. */ @supports(at-rule(@foo)) { /* @foo is supported */ } ``` ```css /* 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(). ```css /* 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 1832769 1 webkit-bug-importer 2022-01-21 08:24:55 -0800 <rdar://problem/87884897> 2044454 2 bramus 2024-07-03 09:45:32 -0700 FYI: I am seeing an uptick in requests for this, especially with `@property` becoming interoperable soon: authors want to detec this. Another request was to detect `@starting-style` support.