[css-shadow-parts][css-view-transitions] Are view transition pseudo-elements allowed after ::part()?

[dbaron]

My understanding of the view transition pseudo-elements is that they are all pseudo-elements on the root element. This means they don't really make sense to be allowed after ::part(), despite that the ::part spec says that all pseudo-elements are allowed after ::part().

If we agree in #10786 that the rules on what is allowed after ::part() are a parse-time restriction, then we probably need to decide whether the view transition pseudo-elements should be allowed. My current inclination is that they probably shouldn't be since they could never match, but I don't have a strong opinion.

[nt1m]

It should probably behave the same way as adding a view transition pseudo-element after a normal element, e.g. parse but not match anything

[tabatkins]

Scoped VTs will allow the VT pseudo-els to be used on elements other than the root, so it'll eventually make sense to be able to use them on ::part().

For now, I indeed think that we should allow them to exist but just not match anything.

[dbaron]

OK, sounds like making no change is the right path here, then.