def add_processor(self, processor_instance: Processor, priority=0) -> None:
        """Add a Processor instance to the World.

        :param processor_instance: An instance of a Processor,
        subclassed from the Processor class
        :param priority: A higher number is processed first.
        """
        assert issubclass(processor_instance.__class__, Processor)
        processor_instance.priority = priority
        processor_instance.world = self
        self._processors.append(processor_instance)
        self._processors.sort(key=lambda proc: proc.priority, reverse=True)
Add a Processor instance to the World.

        :param processor_instance: An instance of a Processor,
        subclassed from the Processor class
        :param priority: A higher number is processed first.