Re: [selectors] Proposal: :n-children() selector

Tab Atkins Jr. skrev:
> That said, I'd actually prefer not to implement this.  Instead, I'd
> prefer to get custom selectors working (at least the declarative alias
> kind) as suggested in
> <http://dev.w3.org/csswg/css-extensions/#custom-selectors>, so people
> can do this themselves if they want it.  Doing this well requires
> going a little further than what is currently written in the doc, but
> all very believable - basically we need a way to handle plumbing
> arguments through from the "custom" pseudo to the expansion, and we
> need some better combinators to handle "self and/or siblings", etc.
>
> With that, you could do something like:
>
> @custom-selector $rest:--n-siblings($n)
> :nth-child(1):nth-last-child($n) /self-and-siblings/ $rest;
>
> So that writing `.foo:--n-siblings(3)` would become
> `:nth-child(1):nth-last-child(3) /self-and-siblings/ .foo` after
> expansion.
>
> ~TJ
>
>
Those selectors look scary. Simplicity helps authors get things right.

There is also a matter of performance. I don't know how to evaluate
performance, but one thing is clear: browsers have the opportunity to
optimize if they know what you are doing.