W3C home > Mailing lists > Public > www-style@w3.org > July 2013

Re: [selectors] Finding a way to run "complete" profile selectors in CSS

From: Boris Zbarsky <bzbarsky@MIT.EDU>
Date: Thu, 11 Jul 2013 21:27:26 -0400
Message-ID: <51DF5B7E.80106@mit.edu>
To: www-style@w3.org
On 7/11/13 7:28 PM, Tab Atkins Jr. wrote:
> Basic issue: we've got cool new selectors in Selectors 4 (and more
> that we'd like to add in future levels) that we aren't allowed to use
> in normal CSS because they're too slow.

I would like to understand clearly what we mean by "slow".

Do we mean that given an element it's slow to determine whether the 
selector matches?

Or do we mean that given a change to some element (e.g. attribute change 
or state change) it's slow to determine the set of elements whose style 
might have changed as a result when selectors like this are present?

Or do we mean both?

Or something else?

> The question then is how we can mitigate the problem that is currently
> preventing us from using them in normal CSS.

I would like to clearly understand the problem first, before we worry 
about how to solve it.

> The issue is that the new selectors are too slow to reasonably run as often as we run other
> selectors

This concept of "running" selectors confuses me.  There is no such thing 
as "running a selector" outside contexts like querySelector.   What a 
CSS implementation has to do is determine the lists of rules that match 
each node and update those lists as needed.  Which of these are you 
trying to do less often here?

> Instead, we add a new function to window.CSS or
> document.CSS or something which requests the browser to run and apply
> the deferred styles

What does that mean, exactly?  Just recompute style on everything in the 
document?  Or something else?

-Boris
Received on Friday, 12 July 2013 01:27:55 UTC

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