code: def process_event(self, event):
          
          for effect in reversed(self._effects):
              event = effect.process_event(event)
              if event is None:
                  break
          return event
docs: Process a new input event.
  
          This method will pass the event on to any Effects in reverse Z order so that the
          top-most Effect has priority.
  
          :param event: The Event that has been triggered.
          :returns: None if the Scene processed the event, else the original event.