sort | uniq via keys

Hello,

I am interested in a sorted and uniqed list of all element names in
an XML file (except for the root), similar to `sort | uniq' in UNIX.

e.g., in the following data,

<db>
   <a>...</a>
   <z>...</z>
   <g>...</g>
   <j>
      <f>...</f>
      <z>...</z>
      <a><o>...</o></a>
   </j>
   <b>...</b>
   <b>...</b>
</db>

I'd like the following list

a
b
f
g
j
o
z

I am trying to achieve this with keys (unless someone can direct me to
a simpler method).  The following is an initial attempt.

<xsl:key name="features" match="*" use="name()"/>

<xsl:template match="/db">

<xsl:for-each select="following::*[count (. | key('features', name())[1]) = 1]">
   <xsl:sort select="name()" />
   <xsl:value-of select="name()" /><xsl:text>
</xsl:text>
</xsl:for-each>

</xsl:template>

<xsl:template match="text()"/>

This is not working out however.  It returns an empty file.  Does this
appear to be correct?

Thank You and Best Regards,

Saverio Perugini


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