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Re: Proposal for limited :matches pseudoclass

From: fantasai <fantasai.lists@inkedblade.net>
Date: Tue, 13 Jan 2009 17:50:03 -0800
Message-ID: <496D44CB.6020604@inkedblade.net>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
CC: www-style list <www-style@w3.org>

Tab Atkins Jr. wrote:
> This is lifted from the :has-child proposal thread, since at least one 
> person (Brad Kemper) liked the syntax, and at least one implementor 
> (Boris Zbarsky) thought it wouldn't be horrible for implementations (at 
> least, no more horrible than current child and sibling combinators).  
> Thought I'd give it a proper write-up, since I've had reason to want it 
> in the last week.
> /:matches pseudo-class/
> The :matches(/selector fragment/) pseudo-class represents an element 
> that has another specified element /after /it in the document tree.  The 
> selector fragment starts with either the child combinator (>) or the 
> adjacent-sibling combinator (+), optionally followed by whitespace, 
> followed by a simple selector (see Selectors Level 3 for the definition 
> of a simple selector).  This matches if an element matched by the simple 
> selector occurs as a child (if > was used) or following adjacent sibling 
> (if + was used) of the target element.  If the selector fragment is 
> invalid or empty, the entire selector is invalid.
> Examples:
>   td:matches(> input:checked) /* Matches any td with a checked input as a direct child */
>   h1:matches(+ ul) /* Matches any h1 which is directly followed by a <ul> */

Going with the original idea that a full :matches() implementation
would match any element that matches its argument selector, you'd
need to write
   elem:matches(* > child)
   :matches(elem > child)
   td:matches(* > input:checked)
   :matches(h1 + ul)

:matches would take a normal selector rather than a fragment that
begins with a combinator (which seems very unbalanced to me, like
passing a mathematical function an expression that began with the
multiplication symbol). It would just be restricted to only allow
the > and + combinators.

An alternative syntax that was proposed many years ago is to add
the ability to change the subject of the selector with some kind
of punctuation, e.g.

   !td > input:checked { ... }
   !h1 + ul { .. }

Again, you can make the same combinator restrictions for anything
after the !. I personally find this easier to read. A syntax like
:matches() is only necessary if you're matching against multiple
branches of the tree.

Received on Wednesday, 14 January 2009 01:50:48 UTC

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