Thanks for your response Ken.

> The first bookmark of the entire set or the first bookmark of the chapter? - I meant the first bookmark of the chapter.

And when I said 'under' I meant nested bookmarks.

The problem I am having is that since the element 'task' can repeat
for a chapter, I am unable to generate the bookmark internal
destination ids to be unique. Since FOP does not support XSLT 1.0 (
and I restricted to this product),  I am not able to use the xslt 2.0
for-each-group to be able to group the tasks. I have to use keys to
group them. Is there any other better way of doing this?

~/t/ftemp $ cat kusa.xml
<?xml version="1.0" encoding="UTF-8"?>
<tasks>

<task chap="8" key="a123" seq="1" pg = "1">
<!-- some more content here-->
</task>

<task chap="8" key="y837458" seq="2" pg = "2">
<!-- some more content here-->
</task>
<task chap="9" key="3jkhkj" seq="1" pg = "1">
<!-- some more content here-->
</task>
<task chap="9" key="t8798" seq="2" pg = "2">
<!-- some more content here-->
</task>
</tasks>
~/t/ftemp $ xslt kusa.xml kusa.xsl
<?xml version="1.0" encoding="utf-8"?>
<bookmark-tree xmlns="http://www.w3.org/1999/XSL/Format">
   <bookmark internal-destination="d0e3">
      <bookmark-title>8</bookmark-title>
      <bookmark internal-destination="d0e8">
         <bookmark-title>8-2</bookmark-title>
      </bookmark>
   </bookmark>
   <bookmark internal-destination="d0e13">
      <bookmark-title>9</bookmark-title>
      <bookmark internal-destination="d0e18">
         <bookmark-title>9-2</bookmark-title>
      </bookmark>
   </bookmark>
</bookmark-tree>~/t/ftemp $
~/t/ftemp $ cat kusa.xsl
<?xml version="1.0" encoding="US-ASCII"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns="http://www.w3.org/1999/XSL/Format"
                version="1.0">

<xsl:template match="tasks">
  <bookmark-tree>
    <xsl:for-each select="task[generate-id(.)=
                               generate-id(key('tasks',@chap)[1])]">
      <bookmark internal-destination="{generate-id(.)}">
        <bookmark-title>
          <xsl:value-of select="@chap"/>
        </bookmark-title>
        <xsl:for-each select="key('tasks',@chap)[position()>1]">
          <bookmark internal-destination="{generate-id(.)}">
            <bookmark-title>
              <xsl:value-of select="concat(@chap,'-',@seq)"/>
            </bookmark-title>
          </bookmark>
        </xsl:for-each>
      </bookmark>
    </xsl:for-each>
  </bookmark-tree>
</xsl:template>

</xsl:stylesheet>~/t/ftemp $
~/t/ftemp $

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