Merging xml files

Using Instant Saxon 6.5.3

I have seen previous posts but a bit comfounded at
getting it to work for me... want to merge identical
xml files using xslt

the following is what I have so far...any help on what
my stylesheet should be would be gratefully received,
thaks.

ctt.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<ctt>
<doc filename="test1.xml"/>
<doc filename="test2.xml"/>
<doc filename="test3.xml"/>
</ctt>

test1.xml - all xml files have the same format

<?xml version="1.0" encoding="ISO-8859-1"?>
<ctt>
<ctt_doc ctt_doc_ref="1">
<parent_doc_ref>testthis</parent_doc_ref>
</ctt_doc>
</ctt>

bad xslt stylesheet...(i.e. not working)

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
 version="1.0">
 
<xsl:output indent="yes"/>
<xsl:template match="ctt">
 <ctt>
  <xsl:variable name="docs"
select="document(ctt/doc/@filename)"/>
  <xsl:for-each select="$docs">
   <xsl:copy-of select="./ctt_doc"/>
   <xsl:copy-of select="ctt/ctt_doc/parent_doc_ref"/>
  </xsl:for-each>
 </ctt>
</xsl:template>
</xsl:stylesheet>

current output upon:
 saxon -o newtest.xml ctt.xml merge.xsl

<?xml version="1.0" encoding="utf-8"?>
<ctt/>

would like...

<?xml version="1.0" encoding="ISO-8859-1"?>
<ctt>
<ctt_doc ctt_doc_ref="1">
<parent_doc_ref>testthis</parent_doc_ref>
</ctt_doc>
<ctt_doc ctt_doc_ref="2">
<parent_doc_ref>testthis</parent_doc_ref>
</ctt_doc>
<ctt_doc ctt_doc_ref="3">
<parent_doc_ref>testthis</parent_doc_ref>
</ctt_doc>
</ctt>