LGTM2 (and thank you for the great explainer).
On 3/12/26 6:33 p.m., Philip Jägenstedt wrote:
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/9743https://ruhr.social/@nilsbinder/112721678680237204https://mastodon.social/@xro/113106213499516093https://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
<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
<https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAARdPYffhV1zUrz8msNPTO-ZN1gVjTRkbfrx%3DW-7pFVMneh%3DPA%40mail.gmail.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/336c5956-27f2-4db6-ac44-c475f953f920%40chromium.org.
