apply-template inside xsl:variable returns a document

I have an xml document in another namespace that I am performing a lookup
on.  The result should be a single node (having attributes and elements).  I
am assigning the result of this lookup to a variable so that the attributes
and elements can be accessed if and when needed without multiple lookups.

My problem is that I am getting the desired node as a child of a
documentFragment.  I haven't a clue as to what a documentFragment is, why am
I getting it, how to get rid of it or otherwise work around it.

Here is the pertinent code:

  <xsl:variable name="elementContent"
select="document('content.xml')/c:content/c:elements"/>
  <xsl:key name="elementContentKey" match="c:element" use="@id"/>

  <xsl:template match="c:elements">
    <xsl:param name="elementName"/>
    <xsl:copy-of select="key('elementContentKey', $elementName )"/>
  </xsl:template>

and then in a template (in which context, @name is valued), I define the
variable $thisContent.

  <xsl:variable name="thisContent">
    <xsl:apply-templates select="$elementContent">
      <xsl:with-param name="elementName" select="@name"/>
    </xsl:apply-templates>
  </xsl:variable>

The file content.xml has a structure like

  <content>
    <elements>
      <element id="table">
        <caption>Table</caption>
        <description>Name of table in database</description>
        <help href="table.help"/>
      </element>
    </elements>
    ...
  </content>

I would like $thisContent to be equivalent to the single <element> shown
above, when @name = "table".


Thanks for any consideration of my problem.


Regards,
John