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[css3-selectors] :nth-child issues

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Tue, 20 Oct 2009 09:57:25 -0500
Message-ID: <dd0fbad0910200757n288ad945u657109cfbe9d1dc1@mail.gmail.com>
To: www-style list <www-style@w3.org>
The relevant text from css3-selectors:

The :nth-child(an+b) pseudo-class notation represents an element that
has an+b-1 siblings before it in the document tree, for a given
positive integer or zero value of n, and has a parent element. In
other words, this matches the bth child of an element after all the
children have been split into groups of a elements each. For example,
this allows the selectors to address every other row in a table, and
could be used to alternate the color of paragraph text in a cycle of
four. The a and b values must be zero, negative integers or positive
integers. The index of the first child of an element is 1.

We noticed two possibles issues in the chatroom today.

First, the prose says an+b matches "the bth child of an element after
all the children have been split into groups of a elements each".
This doesn't work correctly when b=0, as there is either no bth-child
(if we assume that the later sentence about 1-numbering is to be taken
here as well), or it specifies the wrong elements (if we assume
0-numbering).

Second, what should happen when a and b are both 0?  This matches no
elements, since it evaluates to 0 and the first element is 1.
However, Opera drops the rule entirely, rather than keeping it around
as a rule that simply matches nothing.

~TJ
Received on Tuesday, 20 October 2009 14:58:21 GMT

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