[css-scoping] Tree-scoped names in User and UserAgent origins

[lilles]

When implementing tree-scoped names/references, there was a question about how to handle tree-scoped names in the User and UserAgent origins as they are not associated with a tree-scope. The spec [1] should describe the interactions with user and UA origins.

[1] https://drafts.csswg.org/css-scoping-1/#shadow-names

[tabatkins]

Those stylesheets exist in every tree scope, right? (That... might not actually be defined anywhere.)

If it's not defined anywhere, it should be, so the behavior would just fall out.

[lilles]

I haven't found a definition for that. There is a description along those lines for default styles for custom elements: https://drafts.csswg.org/css-scoping/#default-element-styles

So, since they exist in all tree-scopes, I assume the tree-scoped names would then have the tree-scope of the element?

Then there's the question where in the search order for at-rules the UA and user rules would end up:

1. After the author rules in the element's scope
2. After looking up the nested scopes for author rules