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I am using <xsl:key> to identify unique values amongst a set of nodes. However, some of my nodes are nested, and my current implementation is not picking up those values.

Say I have the following XML structure:

<Concepts>
<Concept>
    <Type>A</Type>
</Concept>

<Concept>
    <Type>B</Type>
</Concept>

<Concept>
    <OR>
        <Type>C</Type>
    </OR>
    <OR>
        <Type>D</Type>
    </OR>
</Concept>
</Concepts>

I currently am using the following XSLT1.0 code:

<xsl:key name="types" match="Concepts/Concept" use="Type"/>
<xsl:template match="/">
    <ul>
        <xsl:for-each select="//Concept[generate-id() = generate-id(key('types',Type)[1])]">
            <li><xsl:value-of select="Type"/></li>
        </xsl:for-each>
    </ul>
</xsl:template>

and the result is:

• A


• B

However, I would like the result to be:

• A


• B


• C


• D

Is there any easy solution, or will I have to restructure my XML?