Intent to Ship: CSS at-rule() function for @supports

[Sajid Anwar]

As of Firefox 157, I intend to turn the CSS at-rule() function for the @supports at-rule on by default on all platforms. This can also be used with the CSS.supports() JavaScript method as well as in the supports() function of the @import at-rule. This was developed behind the layout.css.supports.at-rule.enabled preference.

This feature shipped in Blink since Chrome 148. The WebKit implementation is in progress and is currently previewing in Safari Technology Preview 251.

Bugs:

- Bug 1751188 - Implement at-rule for use with @supports

- Bug 2060755 - Set layout.css.supports.at-rule.enabled for release (@supports at-rule())

Standard:

https://drafts.csswg.org/css-conditional-5/#funcdef-supports-at-rule

Intent to Prototype Thread:

https://groups.google.com/a/mozilla.org/g/dev-platform/c/rm53qxu-8xU/m/ZQAycjzeCgAJ