document() question

I have a string in a variable and I want to convert it
to a document via the document() function.

Given the following example, it's obvious that I would 
get an error because document() is treating the variable's contents
as a filename.  

I presume that I am trying to do the
impossible but I thought I would ask anyway.

Thanks in Advance, Terris

G:\xsl>xt doc2.xml doc2.xsl
java.io.FileNotFoundException: \G:\xsl\askldf
 The wizard of OZJava Servlet ProgrammingJohn Coltrane Rage

G:\xsl>type doc2.xml
<BookList>
    <Book id="1"/>
    <Book id="2"/>
</BookList>

G:\xsl>type doc2.xsl
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/XSL/Transform/1.0">

<xsl:output method="xml" indent="yes"/>

<xsl:variable name="source">askldf
 <BookSet>
   <Book id="1"><Name>The wizard of OZ</Name></Book>
   <Book id="2"><Name>Java Servlet Programming</Name></Book>
   <Book id="3"><Name>John Coltrane Rage</Name></Book>
 </BookSet>
</xsl:variable>

<xsl:template match="/BookList">        <!--document element-->
   <BookList>
     <xsl:for-each select="Book">
       <Book id="{@id}">
         <xsl:variable name="id" select="string(@id)"/>
            <!--note you cannot use document($source)/id($id)-->
         <xsl:for-each select="document($source)">
           <xsl:copy-of select="id($id)/*"/>
         </xsl:for-each>
       </Book>
     </xsl:for-each>
   </BookList>
</xsl:template>

</xsl:stylesheet>





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