Re: preceding-sibling reversed ?

> I'm still a bit perplexed. 
that's usually the way with my answers until Jeni re-words them (I don't
know why I bother:-)

> If you evaluate a nodeset in a string context
> then only the first
> node in the nodeset is considered. 

note that node sets are sets so unordered.

If you evaluate in a string context then the first node in document
order is taken.

However within a step position referes to the order in the direction
specified by the axis that started the step.

> following-sibling::div[@class = 'slide']/@id is the same as
> following-sibling::div[@class = 'slide'][1]/@id.

these are the same, yes.

On the other hand, 
> 	preceding-sibling::div[@class = 'slide']/@id is the same as
> 	preceding-sibling::div[@class = 'slide'][last()]/@id.

yes that [last()] is part of a step using a reverse axis.
the "first node" semantics is the same as using (...)[1]

preceding-sibling::div[@class = 'slide']/@id 
if used as a string selects more than one node (potentially)
so it is first evaluated as

(preceding-sibling::div[@class = 'slide']/@id)[1]

which takes the first node from teh set in document order.

in this case, that happens to be the same as

(preceding-sibling::div[@class = 'slide'])[1]/@id

as every div which has a class=slide also has an id attribute, so taking
the first id attribute is the same as taking the first div and then
taking its id.

with the () the [1] is acting on the node set, so uses document order,
but in
preceding-sibling::div[@class = 'slide'][1]
th e[1] is part of the step and so referes to the order specified by the
axis of the step. Note that [] appearing in steps and [] being
predicates on node sets are in fact completely separate parts of teh
Xpath grammar, they just happen to use the same concrete syntax.

David

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