As written on the API docs: An Action Provider Widget is a widget that has declared several actions by using its 'public static function actions()'. After, a Controller can easily import all its declared actions on its 'public function actions()'.
There are some good guides out there explaining how to work with events and the ways to attach them to your components, but none (that I know) explain the following way to configure your events with CAction classes on your controllers the following way.
We all know how good 'gii' automates the code for us and we normally tend to be happy with what that tool offers at the beginning of our Yii learning curve. But as soon as you start working in larger and larger projects, you realize that its code is too repetitive to maintain and having a small pitfall in general actions means to go over and over through them to fix the issues.