LGTM1, this is a clear gap in feature detection, thanks for closing it! On Wed, Mar 11, 2026 at 10:18 PM 'Kevin Babbitt' via blink-dev < [email protected]> wrote:
> *Note: *This feature is a bit unusual in that it was implemented behind a > flag but not advertised on blink-dev with an I2P or dev trial announcement. > I picked it up after initial implementation, got clarity on some open spec > issues, and adjusted the implementation to match CSSWG resolutions. > > *Contact emails* > [email protected] > > *Explainer* > > https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/main/AtRuleFeatureDetection/explainer.md > > *Specification* > https://drafts.csswg.org/css-conditional-5/#support-definition-at-rules > > *Summary* > This feature adds an `at-rule()` function to CSS `@supports` which enables > authors to feature-detect support for CSS at-rules. > > *Blink component* > Blink>CSS > <https://issues.chromium.org/issues?q=customfield1222907:%22Blink%3ECSS%22> > > *Web Feature ID* > supports-at-rule <https://webstatus.dev/features/supports-at-rule> > > *Motivation* > Feature detection is a W3C TAG design principle and a tool that Web > authors rely on for graceful degradation of their pages. Currently, the > only way for web developers to detect support for CSS at-rules is to use > JavaScript. This feature allows at-rule support to be detected using the > same `@supports` feature used to detect support for CSS properties. > > *Initial public proposal* > https://github.com/w3c/csswg-drafts/issues/2463 > > *TAG review* > https://github.com/w3ctag/design-reviews/issues/1176 > > *TAG review status* > Issues addressed > > *Goals for experimentation* > None > > *Risks* > > > *Interoperability and Compatibility* > Minimal risks; this feature is purely additive. > > *Gecko*: No signal ( > https://github.com/mozilla/standards-positions/issues/1310) > > *WebKit*: No signal ( > https://github.com/WebKit/standards-positions/issues/565) > > *Web developers*: Positive There have been several requests for this > feature; some examples: https://github.com/w3c/csswg-drafts/issues/9743 > https://ruhr.social/@nilsbinder/112721678680237204 > https://mastodon.social/@xro/113106213499516093 > https://bsky.app/profile/badrihippo.fosstodon.org.ap.brid.gy/post/3m6vupwqhbkk2 > > *Other signals*: > > *WebView application risks* > *Does this intent deprecate or change behavior of existing APIs, such that > it has potentially high risk for Android WebView-based applications?* > N/A > > > *Debuggability* > Exposure in Dev Tools is the same as for existing `@supports` rules. > > *Will this feature be supported on all six Blink platforms (Windows, Mac, > Linux, ChromeOS, Android, and Android WebView)?* > Yes > > *Is this feature fully tested by **web-platform-tests > <https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>* > *?* > Yes > > https://wpt.fyi/results/css/css-conditional/js/supports-at-rule.html?label=experimental&label=master&aligned > > *Flag name on about://flags* > enable-experimental-web-platform-features > > *Finch feature name* > CSSSupportsAtRuleFunction > > *Rollout plan* > Will ship enabled for all users > > *Requires code in //chrome?* > False > > *Tracking bug* > https://issues.chromium.org/issues/40211832 > > *Estimated milestones* > Shipping on desktop > 148 > DevTrial on desktop > 143 > Shipping on Android > 148 > DevTrial on Android > 143 > Shipping on WebView > 148 > > > *Anticipated spec changes* > *Open questions about a feature may be a source of future web compat or > interop issues. Please list open issues (e.g. links to known github issues > in the project for the feature specification) whose resolution may > introduce web compat/interop risk (e.g., changing to naming or structure of > the API in a non-backward-compatible way).* > No known open issues on `@supports at-rule()` itself. There were some > expansions to the feature discussed to test for certain descriptors or > context, but the CSSWG resolved to separate these more detailed queries out > to a separate feature `@supports-condition`; see discussion at > https://github.com/w3c/csswg-drafts/issues/12622. > > *Link to entry on the Chrome Platform Status* > https://chromestatus.com/feature/5110744177836032?gate=4696535686316032 > > This intent message was generated by Chrome Platform Status > <https://chromestatus.com/>. > > -- > You received this message because you are subscribed to the Google Groups > "blink-dev" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion visit > https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CH4PR00MB2495314F25A2D84629348CC0C047A%40CH4PR00MB2495.namprd00.prod.outlook.com > <https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CH4PR00MB2495314F25A2D84629348CC0C047A%40CH4PR00MB2495.namprd00.prod.outlook.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAARdPYffhV1zUrz8msNPTO-ZN1gVjTRkbfrx%3DW-7pFVMneh%3DPA%40mail.gmail.com.
