Pop Events: Events subscription and notification
An event is identified by a key and its associated parameters. When an event is called using the "$popEvents->call" method, all the listeners registered by the "$popEvents->connect" as callback are notified.
Usage of event help creating pluggable architecture in which new functionnalities could be added and removed whithout altering the overall behavior of the application.
Moreover, events connection can be configured so that no modification of the source code is required to add new functionnalities.