so you just want

<xsl:variable name="sorted">
  <xsl:for-each select="DOCUMENT">
   <xsl:sort select="AUTHOR/>
   <xsl:sort select="ID"/>
   ,xsl:copy-of select="."/>
</xsl;variable>
<xsl:for-each select="exslt:node-set($sorted)">
....

and now docuemnt order and sort order are the same so you can use
preceding-sibling::*[1]/ID to do column 3.


David

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