xsl:attributes strips the "content"
===

I'm writing some rules in Diazo. I want, in case the user browses the "viewer" section (a browser view, not a real plone folder), to drop the "selected" class for the "home" tab in the globalnav and put "selected" class for the "viewer" tab.

    <replace css:content="#portal-globalnav" css:theme="#portal-globalnav" />
    <drop if-path="viewer/" 
    	    css:content="#portaltab-index_html"
    	    attributes="class" />    
    <xsl:template if-path="viewer/"
        	  match="//li[@id='portaltab-viewer']/">
    <xsl:attribute name="class">selected</xsl:attribute>
    </xsl:template>

But the result it's a right li portaltab-viewer with the "selected" class, but without any content inside! I obtain an empty "li" tag in the portal-globalnav O.O

What's wrong?
Vito