<myval><![CDATA[Test5,3]]></myval>

<value>
       <xsl:variable name="currentKey" select="./@Key)" />
       <xsl:variable name="currentVal" select="./Wert" />
       <value_index><xsl:value-of select="my:ownFunction(string($currentKey), string($currentVal), null, 0, '', true, 1)"/></value_index>
</value>