Query Path can be extended to support additional features. To do this, you need only create a new class that implements QueryPathExtension and add your own methods. This class can then be registered as an extension. It will then be available through Query Path.

For information on building your own extension, see QueryPathExtension. If you are trying to load an extension you have downloaded, chances are good that all you need to do is require_once the file that contains the extension.