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@supports selector() feature query function

Category

CSS

Type

New or changed feature

Status

Enabled by default (Chrome 83)

Intent stage

Evaluate readiness to ship

Summary

Adds a function that queries whether a user agent supports a selector.

Motivation

Web authors can use this feature to query whether the UA supports the selector before they actually try to apply the specified style rules matching the selector.

Standards & signals

• Specification: https://drafts.csswg.org/css-conditional-4/#at-supports-ext
• Firefox: Shipped/Shipping — Firefox 69 has shipped this behavior.
• Safari: In development
• Web developers: No signals
• Tracking bug: https://bugs.chromium.org/p/chromium/issues/detail?id=979041

Docs: None.

Samples: The 3 tests below is for testing feature query function of css selector. https://github.com/web-platform-tests/wpt/blob/master/css/css-conditional/at-supports-040.html https://github.com/web-platform-tests/wpt/blob/master/css/css-conditional/at-supports-041.html https://github.com/web-platform-tests/wpt/blob/master/css/css-conditional/at-supports-042.html

Explainers: https://github.com/dbaron/css-supports-functions/blob/master/explainer.md

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