using xsl:key to generate list of back references

The Muench insight rules.

Using TEI markup, where we see things like <ptr target="foo"/> to make 
links, I realized it was easy to get a cross-referenced list of links:

<xsl:key name="targets" match="ptr" use="@target"/>

......
 <xsl:for-each 
     select="//ptr[generate-id(.)=generate-id(key('targets',@target)[1])]">
   <xsl:sort select="@target"/>
   Key <xsl:value-of select="@target"/>
   <xsl:for-each select="key('targets',@target)">
     <xsl:sort select="name(.)"/>
     Referred to in  section  
      <xsl:apply-templates mode="header" select="ancestor::div[last()]"/>
   </xsl:for-each>
 </xsl:for-each>

which generates, eg,

Key history.def
     Referred to in  section  3.2
Key ignores.def
     Referred to in  section  3.1
Key msad
     Referred to in  section  2.1
     Referred to in  section  Appendix A.ii
Key msadac
     Referred to in  section  Appendix A.ii
Key msadad
     Referred to in  section  2.3
     Referred to in  section  2.8
     Referred to in  section  Appendix A.ii

which makes me pretty happy. 

What bothers me is the (relative) inelegance of

 <xsl:for-each 
     select="//ptr[generate-id(.)=generate-id(key('targets',@target)[1])]">

when what I really want to say is something like

 <xsl:for-each select="key('targets','')">

and somehow access the indices of the key structure. Is this
unreasonable of me? The processor has all the information I want,
right to hand, but it forces me to send it off on a wild goose chase
of 
  //ptr[generate-id(.)=generate-id(key('targets',@target)[1])]

which is boring.

Anyone up for Yet Another Extension?

Sebastian Rahtz


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