Creating new Events in YII

While creating a new Event in YII, why do we pass "THIS" object in the constructor ?

for ex, this is an example from YII Cookbook where comment event is being added to POST -

$event = new NewCommentEvent($this);


Check the class manual:

Each event provides the sender (the object which initiated the event) in $event->sender. Therefore you have to supply the sending object to the constructor.