[Bug 22390] [Shadow]: Support ':context()' pseudo class.

https://www.w3.org/Bugs/Public/show_bug.cgi?id=22390

--- Comment #5 from Tab Atkins Jr. <jackalmage@gmail.com> ---
(In reply to comment #4)
> In the f2f on this last Friday, we decided that :host should *not* allow
> combinators, as Tab noted.
> 
> The idea is that from a given shadowRoot, it's important to be able to glean
> some information about the composed tree (for example, does it match an
> important theming selector), but it's brittle to rely on composed tree
> structure (is A inside of B) because its details may change and shouldn't be
> known to a given shadowRoot.
> 
> Hayato-san, in your document, it looks like you're proposing that :host
> allow combinators as long as they match within the host scope. That's an
> interesting restriction and addresses the concern above, but my sense is
> that the additional expressiveness is offset by the arcane host scope
> matching behavior.

Yes, we do *not* want combinators, even if they're just parent or descendant
combinators.  We're matching against the fully composed ancestor list, which
includes the shadow trees of any enclosing components, and we don't want to
expose the details of those trees more than necessary.

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Received on Monday, 24 June 2013 21:40:34 UTC