The dispatching modes describe how the widgets library sends out messages. Currently there are three modes:

xpMode_Direct"0" The message will only be sent to the target widget.
xpMode_UpChain"1" The message is sent to the target widget, then up the chain of parents until the message is
handled or a parentless widget is reached.
xpMode_Recursive"2" The message is sent to the target widget and then all of its children recursively depth-first.
xpMode_DirectAllCallbacks"3" The message is sent just to the target, but goes to every callback, even if it is handled.
xpMode_Once"4" The message is only sent to the very first handler even if it is not accepted. (This is really only useful for some internal widget library functions.)