simplexml_load_string always return a SimpleXMLElement

[Albest]

As described on http://es.php.net/manual/en/function.simplexml-load-string.php,
the second parameter indicates that, provided a clas name derived from
SimpleXMLElement class, this function returns an instance of the
specified className.
As I've seen on the code, this checks for a valid class name provided,
but does nothing with the provided class and returns always a
SimpleXMLElement instance.

If you can provide some guidance, maybe I can try to patch the code...
Sure I'l try it, but I don't know how to instantiate the provided
class Name.

Please, help would be really apreciated.

Best regards.