On Wednesday 2015-02-11 15:05 -0800, Benjamin Poulain wrote: > 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. Those pseudo-classes can be managed separately from general selector matching -- for example, :valid and :invalid are tracked by code managing form validity, which knows about mappings between controls and forms, and can make the form :valid or :invalid based on those mappings, rather than having to do general selector matching. :focus-within can be done the same way. -David -- 𝄞 L. David Baron http://dbaron.org/ 𝄂 𝄢 Mozilla https://www.mozilla.org/ 𝄂 Before I built a wall I'd ask to know What I was walling in or walling out, And to whom I was like to give offense. - Robert Frost, Mending Wall (1914)Received on Wednesday, 11 February 2015 23:44:31 UTC
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