title: xslt 1 and sum function
body: <p>I create an invoice management system using xml and PHP but the latest PHP version does not support XSLT 2.0 - therefore I have to look for an sum() alternative. How can I transform the valid xslt 2 function "sum(unitprice * quantity)" to xslt 1.0 ? </p>
  
  <p>The XML stuff is based on <a href="http://www.objectech.com/exblog/xsl_2.0_invoice.html" rel="nofollow">John's Examples</a></p>
  
  <p>I tried it with a node-set, but it is not supported "xmlXPathCompOpEval: function node-set not found in"</p>