4ca1e4ba_Pattern_for_Event_Notification_son_with_Mediator_and_Observer_Event_Notifier
[0] Informative content of messages [Mediator] Methods may be defined to contain information as desired [Observer] Predefined update() method has no arguments, so no information is carried in the message [Event Notifier] 
Events may be defined to contain information as desired
Event Notifier, a Pattern for Event Notification
Event Notifier