[css-view-transitions-2] Prevent -ua- prefixed idents from parsing in view-transition-name

[nt1m]

Since view transitions generate -ua- prefixed idents, it would make sense to prevent them from parsing to avoid conflicts.

cc @bramus @vmpstr @noamr

[bramus]

Right, this was discussed as part of #12004 (comment) as well (and I forgot to file this issue for it).

[vmpstr]

Sounds good to me.

Proposal: Reserve -ua- prefixes in view-transition-name and make them invalid for users to specify

[nt1m]

cc @emilio from Gecko as well

[emilio]

Sounds good to me.

[emilio]

Hmm, well, are we currently serializing them somewhere tho? Because if so, that's a bit problematic.

[nt1m]

Hmm, well, are we currently serializing them somewhere tho? Because if so, that's a bit problematic.

It's never serialized in view-transition-name, neither in specified or computed style, which use match-element/auto.

However it appears in getAnimations() in the pseudo-element names, and is the "used" value that the engine uses as view-transition-name (but not computed).

[emilio]

Right, ok. I think as long as we don't expose them in getComputedStyle and so we should be fine. Otherwise it'd be weird to serialize something that you can't parse. Thanks!

[astearns]

The CSSWG will automatically accept this resolution one week from now if no objections are raised here. Anyone can add an emoji to this comment to express support. If you do not support this resolution, please add a new comment.

Proposed Resolution: -ua- prefixed idents are invalid for authors in view-transition-name

[astearns]

RESOLVED: -ua- prefixed idents are invalid for authors in view-transition-name