Re: [csswg-drafts] [css-pseudo] clarify paired-cascading behavior (#6386)

> > @delan Wrt which origins disable UA defaults, I'm OK with @emilio's answer as well. Though including the Transitions origin seems weird to me, what if the UA rules want to transition between two styles?

Paired cascade affects used values only, while transitions (and animations) operate in computed value space, so regardless of whether the transition (and/or animation) origin is included, UA transitions (and animations) will behave as if UA default highlight colors were suppressed while they run. If anything, including the transition origin _allows_ UA transitions to work, because if the transition origin _didn’t_ suppress default highlight colors, we would revert to default highlight colors during any UA transition.

@andruud says there are potentially still some problems with treating UA/user-originating transition and animation styles as “author specified” for [native appearance](https://github.com/w3c/csswg-drafts/issues/4777), so if that ends up changing again, we might want to change it here accordingly, but otherwise I don’t think this is a problem for highlight paired cascade.

> So reading [these few comments](https://github.com/whatwg/html/pull/4857#pullrequestreview-424168323), I think the same choice was made for ‘appearance’ because neither Gecko nor Blink are _able_ to tell the difference between a UA transition and an author transition, they are both just transitions? But like ‘appearance’, making transitions suppress UA defaults here improves the experience for authors at the expense of breaking UA transitions? Not sure if I’ve understood that correctly, maybe @andruud and @emilio can correct me.

Yeah, currently in Blink we have no way to tell if some {transition,animation}-origin styles are the result of author transition or UA transition, though we also have no _need_ to do so, as long as our UA stylesheets don’t use any affected transitions/animations.

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Received on Wednesday, 8 December 2021 13:33:47 UTC