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Re: Need test for preceding-sibling

Subject: Re: Need test for preceding-sibling
From: "G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 23 Apr 2009 14:25:51 -0400
Re:  Need test for preceding-sibling
At 2009-04-23 14:01 -0400, Hintz, David L wrote:
I have a structure like this:

<a1/>
<a2/>
<a1/>
<a2/>
<b/>
<c/>
<a2/>
<a1/>
<a2/>

I need to ensure that each <a2> has a preceding <a1>, although there may be intervening tags.

This description is a bit imprecise ... do you need them paired, or will any <a1> before an <a2> suffice?


I ask because in the example you have every <a2> has a preceding <a1>, some with intervening tags and some without.

But it isn't true that every <a2> has a preceding <a1> that follows any preceding <a2>.

I know that

name(preceding-sibling::*[1]

gives me the name of the first preceding sibling, but how do I construct a test that gives me only the first preceding <a1> or <a2> tag?

You shouldn't be working with name() because that deals with strings and not expanded node names in a namespace-safe fashion.


The test that there is any <a1> before the current node being <a2> is:

preceding-sibling::a1

The test that there is an <a1> correspondingly before every <a2> is approached more easily with XSLT 2 grouping from the parent of those siblings:

  <xsl:for-each-group select="*"
                      group-ending-with="a2">
    <xsl:if test="not(current-group()/self::a1)">
       Error!  No corresponding a1 for the given a2
    </xsl:if>
  </xsl:for-each-group>

I hope this helps.

. . . . . . . . . . . . Ken

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