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[csswg-drafts] [selectors-4] Defer complex selectors inside :nth-child() etc. to L5 (#3760)

From: fantasai via GitHub <sysbot+gh@w3.org>
Date: Mon, 25 Mar 2019 23:48:01 +0000
To: public-css-archive@w3.org
Message-ID: <issues.opened-425164423-1553557680-sysbot+gh@w3.org>
fantasai has just created a new issue for https://github.com/w3c/csswg-drafts:

== [selectors-4] Defer complex selectors inside :nth-child() etc. to L5 ==
At the F2F we briefly discussed deferring combinators inside :nth-child() etc. to a future level of Selectors, to make it easier for us to get implementations and interop on the more critical featureset. However, we didn't resolve on the issue. Do we want to do this?

> 
>   [...]
>   fantasai: I think it would make more sense with compound, not complex selectors
>   fantasai: The big question for :nth-child() was compound vs complex selectors.
>   fantasai: people want :nth-child(An+B of <selector>)
>   fantasai: If dropping support for combinators makes it easier, would be good to get it implemented faster. Things like zebra-striping non-hidden rows is a major use case that's not currently solved otherwise.
>   ewilligers: I think webkit already shipped complex selectors in  :nth-child()
>   dydz: I'm looking in the WK code
> 
>   fantasai: Emilio asked why we need selectors in :nth-child()
>   fantasai: Say we have a list of items, I want to color their backgrounds alternately
>   fantasai: But some of them are hidden; they're display:none
>   fantasai: Counting is based on sibling list. If you hide 3rd one, 
>             2nd and 4th will both have the same color
>   fantasai: So want to count after filtering
>   emilio: Whew, that's gonna be slow. We have a lot of caching already to make :nth-of-type() fast.
> 
>   ewilligers: I confirmed that Safari supports :nth-child(even of div+div)
>   fantasai: My main concern is if other impls are more likely to implement without complex selectors, getting even compound-selector interop would still be great.
>   emilio: I think impl-wise, not supporting complex selectors is easier.
>   TabAtkins: Unless we recursively pass down the compound-only restriction into :is()/etc, you're at full power anyway.
>   fantasai: Maybe that's reasonable to have that sort of restriction.
>   fantasai: We'll just say Safari supports L5 of selectors, and L4 doesn't accept combinators
>   <tantek> agreed. reasonable restriction

Possible proposals:
- Do this only for :nth-child() and :nth-of-type()
- Also do this for :is()/:where()/:not()/:has()


Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/3760 using your GitHub account
Received on Monday, 25 March 2019 23:48:03 UTC

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