You don't want to substring the whole of def, just it's first text node
which is text()[1]

so
<xsl:template match="def/text()[1]">
 <xsl:choose>
<xsl:when test="starts-with(.,',')">....

David

________________________________________________________________________
This e-mail has been scanned for all viruses by Star. The
service is powered by MessageLabs. For more information on a proactive
anti-virus service working around the clock, around the globe, visit:
http://www.star.net.uk
________________________________________________________________________