Take a look at http://www.w3.org/TR/xpath#section-Location-Steps
"The initial node-set is filtered by the first predicate to generate a
new node-set; this new node-set is then filtered using the second
predicate, and so on. The final node-set is the node-set selected by
the location step. The axis affects how the expression in each
predicate is evaluated and so the semantics of a predicate is defined
with respect to an axis. See [2.4 Predicates]."
This clearly lays out how multiple predicates are evaluated, and what
their node-set context is.
Try thinking about it as layers of filters.
The first predicate [something] returns a node-set containing only
nodes which have a child element named "something". The second
predicate is operating on this new node-set, so [2] returns the second
node in that list.
Consider the following xml:
<nodes>
<b/>
<b id="1"><something id="1.1"/></b>
<b id="2"/>
<b id="3"><something id="3.1"/></b>
</nodes>
this xsl:
<xsl:copy-of select="/nodes/b[something]"/>
would output
<b id="1"><something id="1.1"/></b>
<b id="3"><something id="3.1"/></b>
this xsl:
<xsl:copy-of select="/nodes/b[something][2]"/>
would output
<b id="3"><something id="3.1"/></b>
Does that help?
Josh
On Fri, 2 Jul 2004 18:24:48 +0100, Kevin Jones <kjones(_at_)sarvega(_dot_)com>
wrote:
I am clearly missing something here or at least not explaining very well.
If we are talking about a pattern,
b[2] - match the 'b' which is the second sibling 'b'
b[something][2] - match the second node that survives the match b[something]
At least that is what I read the standard & earlier quote as saying although I
could clearly be wrong on one or both counts. I suspect both of you are
saying,
b[something][2] - match the 'b' which is the second sibling 'b' if 'something'
evaluates to true.
This is what I understand Saxon to be doing.
The standard explains how the first predicate evaluation starts but is rather
silent on the effect on subsequent predicates. The simplest argument for the
first behaviour is that it is after the first predicate we follow normal
XPath behaviour.
Thanks for your replies,
Kev.
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