The Stylesheet below does most of what I want -- It groups all of the
entries for a single Subject under a single subject heading. I would like

subsort under each group (Subject) first by author then by title, and if
possible, when there is/are no author/authors, by title alone. The example
would put the Kolar book first, then the Siegar Book, both under the single
heading "Catalogs. Austria".

I have spent a lot of time on it but have not been able to solve the sort
within groupings problem. Can someone help?
stylesheet and xml input sample below

Thanks,
Mark

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="2.0">
<xsl:template match="/">
    <List>
        <xsl:for-each-group select="/List/Entry" group-by="Subject">
        <Entry>
            <xsl:copy-of select="Subject"/>
            <xsl:for-each select="current-group()">
                <Item>
                <xsl:copy-of select="*[not(self::Subject)]"/>
                </Item>
            </xsl:for-each>
            </Entry>
        </xsl:for-each-group>
    </List>
</xsl:template>
</xsl:stylesheet>

--------------------------------
- <List>
    - <Entry>
          <Subject>Catalogs. Austria</Subject>
          <Author>Sieger, Hermann Walter</Author>
        - <Book>
              <Title>Zeppelinpost spezial-katalog</Title>
          </Book>
    -  </Entry>
    - <Entry>
      <Subject>Catalogs. Austria</Subject>
      <Author>Kolar, Hugo</Author>
    - <Book>
          <Title>Katalog znamok Rakzsko 1850-1918</Title>
      <Edition>Second</Edition>
      </Book>
      </Locator>
  </Entry>
</List>

<xsl:for-each select="current-group()">
 <xsl:sort select="Author"/>
 <xsl:sort select="Book/Title"/>

This will sort by Author first, then by Book/Title.  If no Author is
present it will just sort by Book/Title.

cheers
andrew