If during an animating view transition you replace the root element, then the originating element of the pseudo-element tree is disconnected, so you can't reasonably do stuff like computing styles with it or what not.

The spec doesn't mention what happens in this case. It probably should skip the transition?

Another alternative could be for the view transition pseudos to be reparented somehow (once / if there's a new root?), but that seems error prone and I don't think there's any use case for that.

Context for it is https://bugzilla.mozilla.org/show_bug.cgi?id=1963212 fwiw.

cc @vmpstr @noamr