Event handler classes.
A abstract class that provides an abstract method that can be called from any event handler. (This is used i.e. for masters and dialog boxes in conjunction with button boxes.)
This is called by an event handler if an event occured (You guessed that. This description is very abstract, because the class is also very abstract).
returns true if a (button) event with the given link string will be handeled. This can be used to gray out the buttons if they shouldn't be used.