vB_XML_Parser how do I?

[Bilderback]

I have searched many sites with no luck.
Can anyone refer me to a decent article or usage of the vB_XML_Parser class?

Thanks

EDIT:
I am attempting to retrieve a local xml file data and have tried:

PHP Code:

require_once (DIR . '/includes/class_xml.php');
$xml = new vB_XML_Parser($xmldata, $file); 


The file exists
But echo or gettype($xmldata) returns NULL