The easiest way is to use Attribute Value Templates (AVT):
Code:
<a href="mailto:agent-{OrderReferences/ProjectCode}@foo.com">Mail</a>
Anything in {} is treated as an XPath expression. (Not all atttributes within xslt support this style.)
You could also create the attribute the long way using xsl:attribute:
Code:
<a><xsl:attribute name="href">mailto:agent-<xsl:value-of select='OrderReferences/ProjectCode'/>@foo.com</xsl:attribute>Mail</a>
--
Joe (
Microsoft MVP - XML)