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Re: Proposal for limited :matches pseudoclass

From: Francois Remy <fremycompany_pub@yahoo.fr>
Date: Fri, 1 Aug 2008 00:08:57 +0200
Message-ID: <AB11C5D9B22E4312A395872C396A73D2@FremyCompany1>
To: "Simetrical" <simetrical@gmail.com>, "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: "www-style list" <www-style@w3.org>

From: "Simetrical" <simetrical@gmail.com>
Sent: Thursday, July 31, 2008 11:43 PM
To: "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: "www-style list" <www-style@w3.org>
Subject: Re: Proposal for limited :matches pseudoclass

>
> On Thu, Jul 31, 2008 at 9:50 AM, Tab Atkins Jr. <jackalmage@gmail.com> 
> wrote:
>> Boris, what are your thoughts on my proposal for a more limited :matches?
>> From your previous explanations, it seems that a simple test for children
>> and following siblings shouldn't be any worse than existing implemented
>> selectors.  Specifically, "foo:matches(+ bar)" seems like it would be
>> exactly as complex to resolve as "foo + bar".
>
>>From Boris' last post, I guess the answer to this is that it's a good
> deal more complex, although maybe manageably.  Every time an element
> is added, you might need to recompute style for its immediately
> preceding sibling.  Of course, if you recompute style for an element
> and it turns out that some inheritable property has changed value, you
> need to recompute style for all its descendants, which could be a lot.
> On the other hand, "foo + bar" recomputes nothing at all.
>
> "foo:matches(~ bar)" would be worse, because it would require
> recomputing style for all preceding siblings.  "foo:matches(> bar)"
> would be still worse, because it would require recomputing style for
> the parent, which could mean also *all* siblings (preceding or
> succeeding).  And "foo:matches( bar)" would be worst of all, because
> it could require recomputing style for all *ancestors*, which would
> include the root element, and therefore *all* elements.

Why ?
foo:matches(bar)
is not more complex that "foo bar". Why should we change the style of the 
:root element ?
The only element that change change of style is "foo", and ONLY IF we add a 
bar element in it
and that there was NO ONE in it before. Same if we delete a BAR in a foo 
that was the only BAR
child of the FOO. But never we must change the style of :root.

:matches is scoped to the element on it it's attached

As sample :

    <span id="s1">
    <div id="d1"><span id="s2"></span></div>
    <div id="d2"></div>

div:matches(span) only match the "d1" DIV.

>
> So a rule like "*:matches( span) { color: red }" would require that
> the style of every single element in the document be recomputed *every
> time* a span is added to the document.  Including during initial
> rendering of the page, and any mutations after that.  Which is
> unacceptable.  And the more limited forms you suggest are still worse
> than current selectors, but possibly manageable if there's a real need
> for them (which AFAICT there isn't).
>
> Am I approximately right here?
> 
Received on Thursday, 31 July 2008 22:09:42 GMT

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