Right now view-transition-group is a bit inconsistent, because:

• nearest and <custom-ident> refer to nesting from the descendant's point of view
• contain refers to nesting from the ancestor's point of view.

Perhaps it would make more sense that nearest and <custom-ident> would also act as contain? I think the discussion in the WG here was sort of saying it but the resolution was ambiguous.

If we do that, what happens when there's an invalid <custom-ident>?

cc @vmpstr @khushalsagar @fantasai, also @ydaniv that raised this concern in the last VT breakout.