Represents a trigger that applies a set of actions in response to an event.
Trigger objects have the Setters, EnterActions, and ExitActions properties that apply changes or actions based on the state of certain properties, while EventTrigger objects start a set of Actions when a specified routed event occurs. For example, you may want to use an EventTrigger to start a set of animations when the mouse pointer is over a certain user interface (UI) control. Unlike Trigger, EventTrigger has no concept of termination of state, so the action will not be undone once the condition that raised the event is no longer true.
More info : http://msdn.microsoft.com/en-us/library/system.windows.eventtrigger(v=vs.110).aspx
