xPath question

[Payam Fard]

Hi all, does anyone know what the following xPath does?

//select[not(//label/@for=./@id)]

Also, what does /@for means here?

Thanks.

[Payam Fard]

Also, what is the difference between //label[@for=...] and //label/@for=...?

Thanks.

[Paul Clapham]

Payam Fard wrote://select[not(//label/@for=./@id)]

It finds all of the elements whose name is "select", which are not in any namespace, and for which the expression in [...] can be coerced to "true".

The expression inside [...] is called a "predicate" and it should be an expression which can be coerced to boolean, as this one is. Ignoring the not() function, the expression is of the form A=B. Note that either side (or both) of such an expression can be a nodeset, and two nodesets are equal if any node in A is equal to any node in B. (At least that's how it is in XPath 1.0; it might be different in XPath 2.0, but that's beyond the scope of what I know.)

Does that get you started? The expression itself looks like somebody made it up as a joke, though.

[Paul Clapham]

Payam Fard wrote:Also, what is the difference between //label[@for=...] and //label/@for=...?

The first selects all "label" elements for which the following predicate is true. The second isn't an XPath expression, at least I don't think it is.

[Paul Clapham]

Payam Fard wrote:Also, what does /@for means here?

It doesn't really mean anything, or rather the question is kind of meaningless because you've chopped a random segment out of an expression. However "label/@for" means "the for attribute of a label element".