Defining an attribute only if not empty

I'm trying to add an attribute to an element, something like this:

<xsl:element name="h1">
	<xsl:attribute name="id"><xsl:value-of select="fm/@id"/></xsl:attribute>
	<xsl:attribute name="class"<xsl:value-ofselect="fm/@class"
		/></xsl:attribute>
</xsl:element>


Now my question is, how can I detect whether an attribute doesnt' have a
value (like, say, @id is empty)?

Thanks,
Carlos

--
Carlos E. Araya
WebCT Project Coordinator - New Media Specialist
Alquist Center for Instrucctional Development
San Jose State University
1 Washington Square
San Jose, Ca 95192-0026

email	: araya@xxxxxxxx (prefered)		| Phone (408) 924 2859
	  elrond@xxxxxxxxxxxxxxxx		| Pager (408) 308 1793
Web	: http://www.sjsu.edu/depts/alquist/	| Fax   (408) 924 2437
	  http://valinor.sjsu.edu/~elrond/	

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