[xsl] Dynamic XPath Expression

["Fraser Goffin" <goffinf@xxxxxxxxxxx>]

Is is possible to build up an XPath expression (as a string) and then use it 
with a select or match. For example :-

If the variable $xPath contained the string value '/root/first'

could I do :-

<xsl:copy-of select='$xPath'/>

I have to say from my initial testing this doesn't appear work and copy-of 
would just return the string itself not evaluate as an XPath expression, but 
I wondered whether there is a way of getting something like this to work ?

What I'm trying to do is compare aspects of one XML instance with another. 
There are a lot of comparisons I need to make and I don't really want to 
hard code in each individual test's XPath in an 'if' statement. So I was 
considering creating templates which match the portions of the document I 
want to compare and from that context recursing through matching each node 
found with the corresponding structure in the other doc :-

Doc 1                                                               Doc 2
====                                                              ====

...                                                                     ...
<Employees>                                                     <Employees>
 <Employee>                                                      <Employee>
   <FName>Fraser</FName>    <-- OK -->                <FName>Fraser</FName>
   <LName>Goffin</LName>    <-- OK -->                <LName>Goffin</LName>
 </Employee>                                                     
</Employee>
 <Employee>                                                      <Employee>
   <FName>Luke</FName>     <-- MISMATCH -->     <FName>Marie</FName>
   <LName>Goffin</LName>    <-- MISMATCH -->    <LName>Smith</LName>
 </Employee>                                                    </Employee>
...                                                                      ...
</Employees>                                                  </Employees>