merging multiple xml files

I have multiple xml files that I wish to merge. An example of the files is
below.  Note that a file
may contain thousands of <detail> nodes.  I want to merge them so that the
clients are grouped together
I have been using a master xml file to try and merge but with no success in
keeping the clients together.
Also, due to the size of the files, is using xsl:copy and xsl:copy-of the
best way to approach this.

Thanks
.

<masterfile>
      <doc filename="file1.xml"/>
      <doc filename="file2.xml"/>
      <doc filename="file3.xml"/>
</masterfile>

<client>
      <name>A</name>
      <subclient>
            <name>a</name>
            <detail>....</<detail>
            <detail>....</<detail>
      </subclient>
</client>

<client>
      <name>A</name>
      <subclient>
            <name>b</name>
            <detail>....</<detail>
            <detail>....</<detail>
      </subclient>
</client>

<client>
      <name>B</name>
      <subclient>
            <name>c</name>
            <detail>....</<detail>
            <detail>....</<detail>
      </subclient>
</client>

<merged>
      <client>
            <name>A</name>
            <subclient>
                  <name>a</name>
                  <detail>....</<detail>
                  <detail>....</<detail>
            </subclient>
            <subclient>
                  <name>b</name>
                  <detail>....</<detail>
                  <detail>....</<detail>
            </subclient>
      </client>
      <client>
            <name>B</name>
            <subclient>
                  <name>c</name>
                  <detail>....</<detail>
                  <detail>....</<detail>
            </subclient>
      </client>
</merged>


 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list