Re: [selectors] Previous-sibling combinator?

On 2/11/15 2:57 PM, Tab Atkins Jr. wrote:
> On Thu, Feb 12, 2015 at 9:52 AM, Benjamin Poulain <benjamin@webkit.org> wrote:
>> On 2/11/15 2:47 PM, Tab Atkins Jr. wrote:
>>> The problem with "giving people enough rope to hang themselves" is
>>> when the mere existence of the feature slows down or complexifies the
>>> engine as a whole, regardless of whether it's used.
>>
>> Can you explain this? Why is that the case?
>
> Because being able to handle style invalidations from arbitrarily high
> up in the tree prevents simplifications that assume that can't happen;
> at minimum, it probably adds branches in the code which can have
> measurable perf effects.

There is nothing special about this case. Such invalidation already 
happen for :valid/:invalid and soon for :focus-within.

Benjamin