[csswg-drafts] [css-variables] Remove "animation taint" when inheriting values (#13933)

tabatkins has just created a new issue for https://github.com/w3c/csswg-drafts:

== [css-variables] Remove "animation taint" when inheriting values ==
[spec link](https://drafts.csswg.org/css-variables/#animation-tainted)

Currently, if a custom property is animated, its value is considered "animation-tainted", and this taint follows it through substitution into other custom properties. An animation-tainted value can't be used in any of the animation properties, as that would create cyclic issues.

In <https://bsky.app/profile/janeori.propjockey.io/post/3migosaiets2y>, @JaneOri points out that this restriction isn't necessary once the custom property value is inherited, as a child can no longer influence how a parent animates. If the custom property only has a discrete set of possible values, you can even use a CQ to manually test and set the values onto a new custom property on the child, *effectively* inheriting it but without the taint. That's a little silly, of course, and doesn't work for continuous-value custom props.

We should probably remove the taint when inheriting. This'll require some rewriting of the concept: as written, the spec today taints *the custom property itself* if it's mentioned in a `@keyframes` rule, not the *value* of a custom property that comes from an active animation. I don't know how browsers actually implement the tainting today, tho.

Thoughts? @lilles @andruud @emilio etc?

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/13933 using your GitHub account


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Received on Friday, 15 May 2026 22:57:38 UTC