Tk_HandleEvent is a lower-level procedure that deals with
window events. It is called by Tcl_ServiceEvent (and indirectly
and in a few other cases within Tk. It makes callbacks to any
window event handlers (created by calls to Tk_CreateEventHandler) that match
eventPtr and then returns. In some cases it may be useful
for an application to bypass the Tk event queue and call
Tk_HandleEvent directly instead of calling Tcl_QueueEvent followed by Tcl_ServiceEvent.
This procedure may be invoked recursively. For example, it is
possible to invoke Tk_HandleEvent recursively from a handler
called by Tk_HandleEvent. This sort of operation is useful
in some modal situations, such as when a notifier has been popped
up and an application wishes to wait for the user to click a button
in the notifier before doing anything else.