The following error:

php: expr.cpp:1435: const class Str & Expression::tostringRef() const: Zusicherung ?(functor == EXF_ATOM) && (type == EX_STRING)? nicht erf?llt.
Abgebrochen                                                     

is produced by the following code:

XML:

<?xml version="1.0"?>
<return>
<a>2</a>
<b>3</b>
</return>

XSL:

<xsl:stylesheet version="1.0"
             xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="return">
       <xsl:variable name="a" select="a"/>
       <xsl:variable name="b" select="b"/>
       <input type="hidden" name="startquery" value="{$a+$b}"/>
  </xsl:template>
</xsl:stylesheet>


PHP:

<?php
 
$xmlSource=join("",file("test.xml"));
$xslSource=join("",file("test.xsl"));
xslt_process($xslSource, $xmlSource, $result);
 
print "\n\n$result";
 
?>