@classmethod
def subsystem_dependencies(cls):
    """The subsystems this object uses.

        Override to specify your subsystem dependencies. Always add them to your superclass's value.

        Note: Do not call this directly to retrieve dependencies. See subsystem_dependencies_iter().

        :return: A tuple of SubsystemDependency instances.
                 In the common case where you're an optionable and you want to get an instance scoped
                 to you, call subsystem_cls.scoped(cls) to get an appropriate SubsystemDependency.
                 As a convenience, you may also provide just a subsystem_cls, which is shorthand for
                 SubsystemDependency(subsystem_cls, GLOBAL SCOPE) and indicates that we want to use
                 the global instance of that subsystem.
        """
    return tuple()
