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Re: [css-selectors] Tagname based substrings

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Thu, 7 Apr 2016 19:41:40 -0700
Message-ID: <CAAWBYDCOxLjRYeW9O7ELTaTaZuCTbb=WFibWaMY7oWfvhpELNQ@mail.gmail.com>
To: Francois Remy <francois.remy.dev@outlook.com>
Cc: Simon Pieters <simonp@opera.com>, "Davis, Greg" <greg.davis@pearson.com>, www-style list <www-style@w3.org>, Marat Tanalin <mtanalin@yandex.ru>
On Thu, Apr 7, 2016 at 12:35 PM, Francois Remy
<francois.remy.dev@outlook.com> wrote:
>> From: Tab Atkins Jr. [mailto:jackalmage@gmail.com]
>> On Thu, Apr 7, 2016 at 4:06 AM, Simon Pieters <simonp@opera.com> wrote:
>> > It seems to me this could be equally useful for attributes, in
>> > particular
>> > data-* attributes.
>>
>> Yeah, it's a pretty long-standing request for data-* attributes.
>>
>> > While we're bikeshedding, a more succinct syntax would be IDENT
>> > DELIM(*) (no allowed whitespace between) so you can do:
>> >
>> >     x-admin-* { ... }
>> >     [data-my-*] { ... }
>>
>> Definitely my preference. Very readable, and it bridges the universal selector
>> nicely - * is just a tagname selector with a wildcard and no prefix.
>>
>> > Performance-wise it seems to me this shouldn't be worse than partial
>> > attribute value selectors, but I could be missing something?
>>
>> I *think* you're right, but we should tag in some implementors.  I've bugged
>> Elliot privately.
>
> I think this would break an optimization some browsers do where they create a bloom filter of attributes being used for css selectors, in order to avoid invalidating the style for most attribute changes. This would make it harder by adding another component on top of the bloom filter. Not sure this is worth the pain. If you control the element, just add a "data-my=true" attribute and test for it.

Yup, this is what Elliot told me today.  We use some data structures
to know what sort of tagnames and attribute names are relevant to
subtrees, so we can tell quickly whether or not a given DOM mutation
needs to recompute the style for the subtree.  Any "fuzzy" matching
like this defeats those optimizations, so their presence will slow
down the performance of the CSS engine on the entire page.

~TJ
Received on Friday, 8 April 2016 02:42:28 UTC

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