[Bug 24872] [Shadow]: Consider adding back at least :first-of-type to valid matching criteria

https://www.w3.org/Bugs/Public/show_bug.cgi?id=24872

--- Comment #5 from Ryosuke Niwa <rniwa@webkit.org> ---
(In reply to Hayato Ito from comment #4)
> (In reply to Ryosuke Niwa from comment #3)
> > (In reply to Jonas Sicking from comment #1)
> > > My concern with this is that it means that anytime that a node is inserted
> > > anywhere, we need to recheck the insertion-point for all of its siblings.
> > 
> > Same concern here. The problem with :first-of-type is that it involves
> > walking previous siblings to check this condition when multiple children are
> > inserted via document fragments.
> 
> Right. I guess this is one of the pseudo classes which is difficult to
> implement without performance impact.
> In general, we need *virtual siblings traversal* for Tree-Structural
> pseudo-classes.
> http://dev.w3.org/csswg/selectors4/#structural-pseudos

I don't think we should be supporting these pseudo selectors in the level 1
specification when we could easily support the use case by adding a simple
imperative API for it given the performance impact.  In fact, such an
imperative API would support more use cases such as an element that picks a
random child element upon click.

I'd go as far as to say we wouldn't implement this even if it were in the spec.

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Received on Thursday, 6 March 2014 15:56:31 UTC