Let's get the terminology correct here, folks.
If you are calling a function that is residing within a class, reference it by its INSTANCE name, NOT its class name.
class.my_class.php:
<?php
class class_name {
static function function_name($in){
return ($out);
}
}
?>
calling_document.php:
<?php
require_once('class.my_class.php');
$instance_name=new class_name();
?>
my_xslt.xsl:
<xsl:value-of select="php:function ('instance_name::function_name','garbage')" />
BTW, in 5.1.6 double-colon (::) is the only thing that works when calling a function that resides within a class. However, you must declare your function as static. Using -> as some have suggested (e.g., php:function ('instance_name->function_name','garbage')) doesn't work at all, no matter how you declare your function.