[xsl] positional predicates in XPath vs XQL

["Howard Katz" <howardk at fatdog dot com>]

I'm implementing an engine that evaluates XPath. I'm currently working on
the part of the engine that implements positional predicates. I've
previously worked this out for location paths in XQL, but I think the
semantics are different in the two languages and want to make sure I
understand the differences.

In XQL if you say (pretending for the moment that positions start from 1 as
they do in XPath, rather than 0):

     /section/para[ 1 ]

and you have a tree that looks like this:

1  section
2       para
3       para
4  section
5       para
6  section
7       para
8       para
9       para

you'll get back this nodeset:

<2>, <5>, <7>

You can paraphrase this XQL query as saying, "Give me back the 1st child
node of each <section> element." Similarly, "/section/para[ 2 ]" returns
<3>, <8>, and if you say "/section/para[ 3 ]", you get back the single node,
<9>.

To my understanding, the same location path in XPath only returns a single
node, <2>. Is my understanding correct?

Howard






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