The algorithm at the start of section 7 "is used to determine whether any given rule is applicable to any DOM node".

Emphasis on *any*.

Per step 2.3.1, If RULE is an author style, in the case TREE is a shadow DOM subtree, if TREE has the apply-author-styles flag is set for TREE, RULE is applicable to NODE.

Does this mean that apply-author-styles should bleed styles from one unrelated, sibling shadow tree to another? This is probably not what is intended and should be clarified.

I think this needs to be more specific. In the case of nested (not stacked) shadow trees, when the outer shadow tree contains <style scoped> and the inner shadow tree has apply-author-styles, do the styles from the outer shadow tree apply to the inner one? Or does apply-author-styles reach into the document? Does it always reach into the document (ie does whether the outer shadow tree have apply-author-styles have any effect on the inner shadow tree?)