Interface for class capable of handling events.
| HandleEvent | Handles an event according to its propagation phase and current target, by executing the element's default action, default action at target, or callbacks associated with the event. |
| HasBubbleUpHandlers | Returns true if event handlers for the event propagation BubbleUp phase, have been attached on this object. |
| HasTrickleDownHandlers | Returns true if event handlers, for the event propagation TrickleDown phase, are attached to this object. |
| SendEvent | Sends an event to the event handler. |