MacroCommand, Command, Mediator and Proxy all have a need to send Notifications.

The Notifier provides a common method called send_notification that relieves implementation code of the necessity to actually construct Notifications.

The Notifier class, which all of the above mentioned classes extend, provides an initialized reference to the Facade Singleton, which is required for the convienience method for sending Notifications, but also eases implementation as these classes have frequent Facade interactions and usually require access to the facade anyway.