This method adds an association between a clipboard format such as "#1" (special name for Plain Text) and a particular class name such as WPDataFile. This is used in the paste-to-folder function to decide which classes support a particular rendering format.

This method is usually called in wpclsInitData when an object class is registered for the first time.

Note: You should block the call to this method with a static variable which forces it to only be called once. Otherwise, it will execute the same code when the object's subclasses are registered.