Keeping an eye on processed nodes

I'm doing something really wrong here. I'm trying to process an index for a
book, and find myself in a situation where I need to keep an eye on which
nodes I have already processed. Since this is not possible in XSLT, I need
your help to find an alterntive solution. Part of the XML:

<?xml version="1.0" encoding="iso-8859-1"?>
<index>
  ...
  <entry page="34">A4 page size</entry>
  <entry page="37">absolute direction</entry>
  <entry page="172" context="absolute-position property">correcting
    content position with</entry>
  <entry page="91" context="absolute-position property">offsetting
    content with</entry>
  <entry page="139">alignment points</entry>
  ...
</index>

This should be rendered as:

A4 page size, 34
absolute direction, 37
absolute-position property
  correcting content position with, 172
  offsetting content with, 91
alignment points, 139

The entry template in the XSL file:

  <!-- TM: Index entries -->
  <xsl:template match="entry">
    <xsl:variable name="context" select="@context"/>
    <xsl:choose>
      <!-- If the entry has a certain context... -->
      <xsl:when test="@context">
        <!-- ...print the context, then... -->
        <fo:block xsl:use-attribute-sets="entries">
          <xsl:value-of select="@context"/>
        </fo:block>
        <!-- ...print each entry within this context -->
        <xsl:for-each select="//entry[(_at_)context = $context]">
          <fo:block xsl:use-attribute-sets="entries">
            <xsl:attribute name="margin-left">1em</xsl:attribute>
            <xsl:call-template name="print-entry"/>
          </fo:block>
        </xsl:for-each>
      </xsl:when>
      <!-- If the entry has no context -->
      <xsl:otherwise>
        <fo:block xsl:use-attribute-sets="entries">
          <xsl:call-template name="print-entry"/>
        </fo:block>
        <!-- Look for other entries with this context -->
        <xsl:for-each select="//entry[(_at_)context = text()]">
          <fo:block xsl:use-attribute-sets="entries">
            <xsl:attribute name="margin-left">1em</xsl:attribute>
            <xsl:call-template name="print-entry"/>
          </fo:block>
        </xsl:for-each>
      </xsl:otherwise>
    </xsl:choose>
  </xsl:template>

The problem occurs when several words are grouped. For each entry within
the same @context, a new group is made, like this:

absolute-position property
  correcting content position with, 172
  offsetting content with, 91
absolute-position property
  correcting content position with, 172
  offsetting content with, 91

Another related problem occurs on entries without @context, but other
entries with matching @context attributes, like this:

<entry page="129-132">background-color property</entry>
<entry page="94" context="background-color property">images and</entry>

This should be rendered as:

background-color property, 129-132
  images and, 94

For each new entry, I check if there are any entries with a matching
@context and list them below. But the result is:

background-color property, 129?132
background-color property
  images and, 94

Gustaf



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