The FXTriStateButton class provides a three-state button, which toggles between the on and the off state each time it is pressed. Programmatically, it may also be switched into the MAYBE state. The MAYBE state is useful to signify an "unknown" state in the application data. Like FXToggleButton, it sends a SEL_COMMAND message to its target, with the message data set to the current state of the button (with type FXbool).