Re: [xsl] Need test for preceding-sibling

["G. Ken Holman" <gkholman@xxxxxxxxxxxxxxxxxxxx>]

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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