[xsl] Single output from many inputs

[David Sinclair <dsinclair@xxxxxxxxxxxx>]

I have an ant build file and one of the tasks we need to do is to 
collect all the elements that have a certain attribute across many files 
in our code base into one xml file.  

Does anyone here know of a way to use XSLT to do this?  I had thought to 
use the xslt ant task to run on all files with a certain extension and 
collect all the values but I cant find a way to collect the results of 
each transform into the same file.

       <xslt basedir="${sourcedir}" destdir="${targetdir}"
           style="extract-shared-instances.xsl" includes="**/*.xhtml"
           extension=".xhtml" force="true"/>

Thanks in advance for any assistance you can give me,

Dave