An event is the mechanism that notifies the application when the user performs a mouse or keyboard operation. The application can be notified about key presses and releases, mouse button presses and releases, and mouse movements. Events are handled by adding an event handler to a widget.

A callback is the mechanism that notifies the application when some higher level action is performed on a widget. For example, the XmNactivateCallback is used to inform the application that a CwPushButton has been pressed and released. As another example, all widgets support the XmNdestroyCallback that is invoked just before a widget is destroyed.

The following example illustrates how callbacks and event handlers are defined. For detailed information on callbacks and event handlers, see "Callbacks" and "Event handlers".