[css-scoping] :scope > * matches nothing in shadow trees

[andruud]

In #7261 (cc @emilio), @tabatkins concludes that:

myshadowroot.querySelector(":scope > *") returns all the root nodes in the shadow tree.

But no it doesn't: in the context of a shadow tree, the shadow root is specified to be replaced by the shadow host for the purposes of selector matching. This means that the node :scope represents here doesn't exist as far as selector matching is concerned. https://drafts.csswg.org/css-scoping-1/#host-element-in-tree

[tabatkins]

Oof, that's an accidental interaction. Maybe we can just special-case that and say that, when calling querySelector() on a shadow root, the :scope represents the shadow host.

(The shadow root is, itself, not selectable anyway, as it doesn't exist in the tree as far as Selectors is concerned.)

[sorvell]

Is this issue related / the same? #11000 (comment)

[andruud]

@sorvell I think that's definitely close enough, thanks.

Closing as duplicate of #11000.