[csswg-drafts] [css-variables] Disallow animation-tainted substitutions in any non-animatable property (#5341)

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

== [css-variables] Disallow animation-tainted substitutions in any non-animatable property ==
Currently, if a custom property is animation-tainted, it's [not allowed to substitute](https://drafts.csswg.org/css-variables/#substitute-a-var) that custom property into `animation-` properties, nor the `display` property (with some conditions).

This means (since it's not mentioned), that it's allowed to substitute an animation-tainted custom property into `direction` and `writing-mode` (among others), effectively making those properties animatable. This makes it unnecessarily complicated to specify a reasonable behavior for css-logical properties in animation keyframes, since the physical properties involved change during the animation.

Properties are probably 'not animatable' [for a reason](https://drafts.csswg.org/web-animations/#not-animatable), so it seems bad to create a loophole where unwanted complexity can "escape".

I propose that we (unconditionally) disallow animation-tainted custom property substitutions in any property that's 'not animatable'.

For what it's worth, Chrome already has this behavior (possibly since the beginning), and I've seen no complaints.

Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/5341 using your GitHub account

Received on Monday, 20 July 2020 18:46:21 UTC