PHP5 XSL Transformation Difficulty

[rastrol7]

I'm trying to use PHP's built in parser to create an HTML file from an XML document and an XSL stylesheet. Everything works except for one line in the XSL. When I comment it out, the php file works perfectly. The line of XSL is:

 

 <xsl:value-of select="sum($price+$add)"/> 

 

I've tested the entire XSL stylesheet on the Saxon8B parser outside of php. But I'm unfamiliar with how to check what parser php uses and how to change it if necessary. Can anyone with more experience in this help me?

 

THANKS!