Re: [selector-profiles] confusion

On Thu, Jul 11, 2013 at 11:33 AM, Lea Verou <lea@w3.org> wrote:
> On Jul 11, 2013, at 21:26, "Tab Atkins Jr." <jackalmage@gmail.com> wrote:
>> And yeah, I see the value of it even for existing
>> selectors like :hover.
>
> ...which is? I thought existing selectors are very fast anyway so any additional optimization is premature optimization.

They're not always.  For example, Blink/Webkit won't update :hover
styling if an element moves under the mouse without the mouse itself
moving, which can happen due to scrolling, animations, etc.  (Or maybe
we recently changed that?  I dunno.)

> In any case, if whatever mechanism we come up with applies to selectors in general, it should be done in a way that older browsers still apply these selectors (i.e. an @rule wouldn't be a good idea).

That seems impossible.  There's nothing we can add to a selector to
indicate this that wouldn't be rejected as invalid by older browsers.

~TJ