Say you have 2 properties in your synapse config. Then you want to pass them to XSLT and refer it from there. So inside the synapse config,
<property name="email" expression="//request/email"/>
<property name="name" expression="//request/name"/>
<xslt key="orderTransformer">
<property name="email" expression="get-property('email')"/>
<property name="name" expression="get-property('name')"/>
</xslt>
Now insdie the XSLT here is how you refer them. First Define them as two params.
<xsl:param name="email"/>
<xsl:param name="name"/>
Use them as $email, $name in where u need.
Example XSLT
<xsl:stylesheet
version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:ns1="http://wso2.org/sample/shop/order">
<xsl:output method="xml" omit-xml-declaration="yes"/>
<xsl:param name="email"/>
<xsl:param name="name"/>
<xsl:template match="/">
<xsl:apply-templates select="//ns1:AddOrder"/>
</xsl:template>
<xsl:template match="ns1:AddOrder">
<ns1:AddOrder>
<ns1:email>
<xsl:value-of select="$email"/>
</ns1:email>
<ns1:name>
<xsl:value-of select="$name"/>
</ns1:name>
</ns1:AddOrder>
</xsl:template>
</xsl:stylesheet>