Many applications can implement their entire input processing by adding procedures to widget callback lists and by adding mnemonics and accelerators for menu buttons.
Some applications change translations, accelerators, or actions.
More rarely, an application needs finer control over event processing. Such an application can register an event handler with the Xt event dispatcher. An event handler is a procedure that the Xt event dispatcher calls when the application receives events of one or more types. An event handler procedure is of type XtEventHandler . This argument is initialized to True and should rarely be changed.