Re: [csswg-drafts] [css-selectors] has-child selector (#4903)

Regarding performance cost, it's more similar to indirect adjacent or :nth-* selectors than direct sibling selectors. In Blink, invalidation sounds straightforward, quite similar to how we invalidate for the previously mentioned selectors.

:nth-selectors are typically implemented with a cache (at least Blink and Gecko/Servo) to avoid repeated O(n) traversals for multiple siblings. :has-child() would only be done once for a set of siblings, since they can only have a single parent, but if you have multiple :has-child() selectors matching the same element, we would possibly want to avoid multiple passes over the children somehow for :has-child().

The current spec text for :has() does not limit this to the rightmost compound. It's not obvious to me that: "div a:has-child(img) span {}" does not have more performance implications than only allowing :has-child() in the rightmost compound.

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Received on Friday, 27 March 2020 09:20:53 UTC