I don't think you can do what you want whilst still using named attribute sets. Without them you would have:
Code:
<tr>
<xsl:choose>
<xsl:when test="$ExcelOutput='Excel'">
<xsl:attribute name="onmousedown">MyRowHighlight();</xsl:attribute>
</xsl:when>
<xsl:otherwise>
</xsl:otherwise>
</xsl:choose>
</tr>
To cope with the use-atribute-sets you could have a named template that just adds thesee in and call it from within the choose statement.
--
Joe (
Microsoft MVP - XML)