Subject: Determining the position of a specific node in the context
From: "Christian Roth" <roth@xxxxxxxxxxxxxx>
Date: Fri, 20 Oct 2006 01:23:54 +0200
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Using: XPath 1
The task: I want to determine if in the current context, a node with
certain properties comes before another.
Example:
<root>
<A/>
<B/>
<C/>
</root>
I want to know whether <B/> comes before <C/>. So I thought, I would
check whether the context position of <B/> is less than the context
position of <C/> in the context made up of select="/root/node()".
My first try:
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
<xsl:template match="root">
<xsl:if test="node()[self::B]/position() < node()[self::C]/position()">
<xsl:message>B comes before C.</xsl:message>
</xsl:if>
</xsl:template>
This gives an error in XSLT1 processors (Xalan, Saxon 6) saying position
() is not a valid element test. (It sure is not.)
[Side note: Testing the above in Saxon 8 (XSLT2, XPath2) does not give
an error or warning, but the test simply evaluates to false. So, "node()
[self::B]/position()" must be a legal XPath 2 expression - what does it
actually do?]
So I am back to the basic question, "How do I retrieve the position of a
certain node in the context?"
Next try:
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
<xsl:template match="root">
<xsl:if test="count(B[1]/preceding-sibling::node())
< count(C[1]/preceding-sibling::node())">
<xsl:message>B comes before C.</xsl:message>
</xsl:if>
</xsl:template>
This actually works, but it looks really cumbersome to me.
Is there a better way to do this?
Regards, Christian.
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