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Re: Specificity: nth-of-type versus attribute selector?

From: Anton Prowse <prowse@moonhenge.net>
Date: Sun, 04 Jul 2010 18:32:38 +0200
Message-ID: <4C30B7A6.1060409@moonhenge.net>
To: www-style@w3.org
CC: "L. David Baron" <dbaron@dbaron.org>, Estelle Weyl <estelle@weyl.org>
L. David Baron wrote:
> On Sunday 2010-07-04 10:24 +0200, Anton Prowse wrote:
>> "Specificity" isn't the right term here (it has another meaning in CSS
>> Selectors [3]) but I understand what you're asking.  However, there is
>> no universal common behaviour of pseudo-classes as regards their
>> interaction with other parts of the sequence of simple selectors to
>> which they belong.
>>
>> Hence we must turn to the definition of the :not pseudo-class to
>> discover its behaviour:
>>
>> "The negation pseudo-class, :not(X), is a functional notation taking a
>> simple selector (excluding the negation pseudo-class itself) as an
>> argument. It represents an element that is not represented by its
>> argument."[4]
>>
>> So, in the sense you mean, the :not pseudo-class does behave differently
>> from the :nth-of-type pseudo-class in that the whole of the simple
>> selector argument is taken into consideration.
> 
> I think this is a confusing way to describe things.  I think it's
> clearer to simply say that the parts of the simple selector are
> independent of each other, and then the results are combined.  Thus:
> 
>   :nth-of-type(5) selects any p element that is the fifth p element
>   within its parent, any div element that is the fifth div element
>   within its parent, any i element that is the fifth i element
>   within its parent, etc.
> 
>   p selects any p element.
> 
>   p:nth-of-type(5) selects the intersection of those two sets, which
>   is any p element that is the fifth p element within its parent.
> 
> Thus, if you add attribute selectors to the same simple selector,
> you're not changing what :nth-of-type() means, you're just
> intersecting the result with an additional restriction.

Yes, I fully agree that intersection is the right way to view this (and
was planning to say so should Estelle have replied; this formulation
only occurred to me seconds after pressing Send ;-)

img[src*="photo"]:nth-of-type(odd)

is the set of elements E which satisfy all of the following properties:

E is an img element
E has a src attribute whose value features the substring "photo"
E is the first or third or fifth or ... element of its type (ie img) of
its parent.


But what I was trying to emphasize in my comment is that :not is in some
sense more powerful than nth-of-type pseudo-class.  If nth-of-type was
renamed slightly (nth-of-specialized-kind ?!) and took a simple selector
as an argument as well as the an+b notation, then it would behave a bit
more like :not (as well as addressing the problem which I think Estelle
wanted to solve).

Cheers,
Anton Prowse
http://dev.moonhenge.net
Received on Sunday, 4 July 2010 16:34:38 GMT

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