Event handlers protocol. The handlers are automatically by the runtime called for messages sent using the ::/2 control construct from within objects compiled with the “events” flag set to “allow”.
(no dependencies on other entities)
Event handler for “before” events. A “before” event handler may prevent a method from being looked up or called by failing.
Event handler for “after” events. An “after” event handler may prevent a method from succeeding by failing.