Intent to Ship: named-feature() function for CSS @supports

[David Baron]

Contact emails

dba...@chromium.org

Explainer

https://github.com/w3c/csswg-drafts/blob/main/css-conditional-5/named-feature-explainer.md

Specification

https://drafts.csswg.org/css-conditional-5/#typedef-supports-named-feature-fn

Summary

The named-feature() function allows CSS @supports rules to query for a small set of specific named features that are not possible to test for using other @supports mechanisms but which are considered highly valuable to test for.

Blink component

Blink>CSS

Web Feature ID

Missing feature

Motivation

Sometimes we add new features to CSS where two things are simultaneously true: first, that CSS authors see high value in writing conditional styles for whether the feature is supported using @supports, and second, that the existing mechanisms in @supports don't provide a useful way to test for the feature.

This provides a way for us to give names to a small number of high-value features so that CSS authors can test for them in their style sheets.

We will ship initially with a single supported feature, identified by the anchor-position-follows-transforms keyword.

Initial public proposal

https://github.com/w3c/csswg-drafts/issues/3559#issuecomment-1868169502

TAG review

https://github.com/w3ctag/design-reviews/issues/1186

TAG review status

Issues addressed

Goals for experimentation

None

Risks

Interoperability and Compatibility

No information provided

Gecko: No signal (https://github.com/mozilla/standards-positions/issues/1340)

WebKit: No signal (https://github.com/WebKit/standards-positions/issues/600)

Web developers: Positive (https://github.com/w3c/csswg-drafts/issues/3559) In various forums developers have asked questions about how to feature-detect things in CSS that we couldn't previously offer feature detection for. While some developers have asked for more powerful feature detection (that would be difficult for us to provide), this provides a simple solution for something developers have been asking for.

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?

No information provided

Debuggability

No information provided

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?

Yes
https://wpt.fyi/results/css/css-conditional/at-supports-named-feature-001.html

Flag name on about://flags

No information provided

Finch feature name

CSSSupportsNamedFeatureFunction

Rollout plan

Will ship enabled for all users

Requires code in //chrome?

False

Tracking bug

https://issues.chromium.org/353715317

Availability expectation

Hoping that other engines will implement soon after launch in Chrome, although we haven't seen concrete signs of this yet.

Adoption expectation

I'd expect that once this is available it will be quickly become a best practice for feature detection of future new features that are given feature names as they roll out to developers.

Adoption plan

Adoption is really tied to the adoption of the other features that this is used to feature-detect.

Estimated milestones

Shipping on desktop	150
DevTrial on desktop	146
Shipping on Android	150
DevTrial on Android	146
Shipping on WebView	150

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 information provided

Link to entry on the Chrome Platform Status

https://chromestatus.com/feature/5153932394102784?gate=4891886507261952

Links to previous Intent discussions

Intent to Prototype: https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAG0MU3ih_y_Z1CVCKHCzK1Sq08HxAc3cvqwpPZrc6%3DB%3DPacz6A%40mail.gmail.com

This intent message was generated by Chrome Platform Status.