On a slightly different note does attempting to parameterise the
separator like this qualify as a gotcha.

The separator is meant to be ":" (3 characters not one) I ended up
defining it in a variable.?

    <xsl:template match="*">
       <xsl:param name="delim" as="xs:string" select='":"'/>
       <xsl:text/>"<xsl:value-of select="if (contains(local-name(),'__')) then

substring-after(local-name(),'__') else
                                                 local-name()
                                                 ,."
                                      separator="{$delim}"/>"<xsl:text/>

    </xsl:template>