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Re: small selector syntax addition

From: Ian Hickson <ian@hixie.ch>
Date: Mon, 06 May 2002 02:32:01 +0100
Message-ID: <3CD5DD11.8050902@hixie.ch>
To: fantasai <fantasai@escape.com>
CC: www-style@w3.org
fantasai wrote:
> Ian Hickson wrote:
>> fantasai wrote:
>>> Ian Hickson wrote:
>>>> :matches() in this idea is exactly equivalent to :matches() in my
>>>> proposal, after moving any selectors associated with the subject
>>>> of the argument out to the level of the :matches() pseudo, and
>>>> replacing the subject with a #.
>>> You also wrote:
>>>>      /* select all fleas if the document contains an antiflea element */
>>>>      flea:matches(antiflea)
>>> which indicates otherwise, since in the syntax I describe that would
>>> match exactly nothing. They are not equivalent, they are merely
>>> similar.
>> Please reread exactly what I wrote. I stand by my original comment.
> I did. I stand by my original reply. :)

Ok, in that case I am very confused. Your comment ("in the syntax I describe 
that would match exactly nothing") doesn't seem relevant, since I didn't say 
that my old :matches() was equivalent to your :matches(), I said the opposite 
(your :matches() was equivalent to my old :matches() after some algorithmic 
changes).


>> Taking your comments into account, here is an updated version of my
>> proposal.
 >>
>>     The special symbol '#' in the argument is a placeholder that
>>     matches the node that the pseudo-class is being tested on. If it
>>     is not used then the last sequence of simple selectors in the
>>     selector chain has to match the element. In other words,
> 
> I don't like the use of # because it normally indicates the start
> of an ID selector. It complicates parsing, both for the computer
> and the person. I know you don't want to use up more symbols, but
> I think in this case the benefit outweighs the advantage.

It doesn't complicate parsing that much. If your sequence of simple selectors 
consists of exactly '#' then you have the special symbol, otherwise '#' will 
mean the start of an ID. Considering how trivial that is, I don't think it's 
worth using a whole other symbol.

Also, the '#' symbol makes more sense to me... it's like an anonymous ID, if you 
see what I mean. It conveys to me that this is something important.

The '$' symbol doesn't really convey anything to me, except maybe something to 
do with sections (BCPL used $(...$) as section markers, and I've been looking at 
BCPL recently...).

I just noticed that the '#' character also looks like a placeholder more than a 
'$' character -- compare:

    A:matches(B + # + C)

    A:matches(B + $ + C)


>>     If the # form appears anywhere except the end of an argument, then
>>     the document must be walked looking for matching elements.
> 
> This sentence is unnecessary.

Where else does it say how to handle a '#' somewhere other than at the end?


>>     The :has() pseudo-class is an alias for :matches(), as follows:
>>
>>        :has(FOO1, FOO2, ..., FOOn)
>>
>>     ...is exactly equivalent to
>>
>>        :matches(# FOO1, # FOO2, ..., # FOOn)
>>
>>     ...in terms of interpretation as a selector. Note that the FOOs
>>     can start with a combinator, if they don't then the descendant
>>     combinator is assumed. This is the same as the way we have 'odd'
>>     and 'even' as equivalents to '2n+1' and '2n' for the :nth-child()
>>     pseudo-classes. It makes the simple case simple.
> 
> I suggest you get rid of this :has(). It's redundant,

Selectors have lots of redundancy, that's not a big problem. For example, '2n+1' 
and 'odd' mean the same thing, and ':first-child' is the same as 
':nth-child(1)'. This is a feature, not a bug. It means that the simplest cases 
are the simplest to write.


 > and starting an argument with a hanging combinator is, to me, far worse than
 > using a subject indicator in the main selector. A:has( + B) looks to me very
> awkward -- it's incomplete -- and reading it doesn't make much sense, either.

Read the "+" combinator as "sibling" and it reads as "an A, which has sibling 
B", just like A.B reads as "an A, whose class is B".

I think it looks better than A:matches(# + B). Also, the most common case of 
looking for descendant doesn't appear to have a hanging combinator:

    p:has(strong)

-- 
Ian Hickson
``The inability of a user agent to implement part of this specification due to
the limitations of a particular device (e.g., non interactive user agents will
probably not implement dynamic pseudo-classes because they make no sense
without interactivity) does not imply non-conformance.'' -- Selectors, Sec13
Received on Sunday, 5 May 2002 21:32:05 GMT

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