The definition of the exslt:node-set() function as currently found on
http://www.exslt.org/exsl/functions/node-set/index.html is:

"The exsl:node-set function converts a result tree fragment (which is
what you get when you use the content of xsl:variable rather than its
select attribute to give a variable value) into a node set. This
enables you to process the XML that you create within a variable, and
therefore do multi-step processing. 

You can also use this function to turn a string into a text node, which
is helpful if you want to pass a string to a function that only accepts
a node set."

This function's behaviour is underspecified in the sense that different
implementations may exhibit quite different behaviours and thus a
transformation using the exslt:node-set() may be non-portable accross
different XSLT processors implementing EXSL.

For example, the following does not raise a run-time error using Saxon
6.5:

    <xsl:template match="str-split2words-func:*"> 
      <xsl:param name="arg1" select="/.."/> 
      <xsl:param name="arg2"/> 
         
<!--1-->  <xsl:copy-of select="exslt:node-set($arg1)/*[1]"/>
<!--2-->  <xsl:copy-of select="$arg1/word[position() != last()]"/>
      
      <xsl:choose> 
<!--2--> <xsl:when test="contains($arg1/*[1], $arg2)">
<!--2-->    <xsl:if test="string($arg1/word[last()])">
<!--2-->       <xsl:copy-of select="$arg1/word[last()]"/>
           </xsl:if> 
          <word/> 
        </xsl:when> 
        <xsl:otherwise> 
          <word> 
            <xsl:value-of 
<!--2-->       select="concat($arg1/word[last()], $arg2)"/>
          </word> 
        </xsl:otherwise> 
      </xsl:choose> 
    </xsl:template> 


When the above template is instantiated passing to it an RTF as the
value of its parameter $arg1, Saxon 6.5 does not signal any error on
the lines starting with <!--2--> 

Recently Michael Kay provided in 
http://sources.redhat.com/ml/xsl-list/2002-05/msg00928.html 
the following explanation of this behaviour:

"Dimitre, you have discovered a feature in Saxon which I have never
advertised. The saxon:node-set() function really does convert an RTF to
a node set. That's right, it doesn't create a node-set that is a copy
of the RTF, it really changes the RTF into a node-set, so once you have
called saxon:node-set($rtf) you can thereafter use $rtf as a node-set.

(In fact, saxon:node-set() simply unsets the bit that says "the user
isn't allowed to do useful things with this tree").

It might seem a very un-functional way of doing things, but it's
perfectly conformant, because extension functions are allowed to have
side-effects." 

The problem is, that other XSLT processors interprete the lines
starting with <!--2-->  as an attempt to manipulate an RTF as a node-set
and raise an error. 

The present definition of exslt:node-set() does allow such different
behaviour.

Therefore, an XSLT transformation using exslt:node-set() will be
applied successfully on Saxon 6.5 and this same transformation will end
abnormally on other XSLT processors.

This is exactly the opposite of what EXSL was defined to achieve.

In order to correct this situation, I propose the definition of
exslt:node-set() to be changed:

"The exsl:node-set function takes an argument, which is a result tree
fragment and returns a node set, which has exactly the same structure,
names and values nodes. The exslt:node-set() function does not have
side effects, e.g. it does not change the its argument".

Cheers,
Dimitre Novatchev.



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