The nsIDOMEventListener interface is a callback interface for
listening to events in the Document Object Model.
For more information on this interface please see
http://www.w3.org/TR/DOM-Level-2-Events/
This method is called whenever an event occurs of the type for which
the EventListener interface was registered.
| evt | The Event contains contextual information about the event. It also contains the stopPropagation and preventDefault methods which are used in determining the event's flow and default action. |