The predicate procedure and its associated arguments are:
Bool (*predicate)(display, event, arg)
|display||Specifies the connection to the X server.|
|event||Specifies the XEvent structure.|
|arg||Specifies the argument passed in from the XIfEvent(), XCheckIfEvent(), or XPeekIfEvent() function.|
The predicate procedure is called once for each event in the queue until it finds a match. After finding a match, the predicate procedure must return True. If it did not find a match, it must return False.
To check the event queue for a matching event and, if found, remove the event from the queue, use XIfEvent().
To check the event queue for a matching event without blocking, use XCheckIfEvent().
To check the event queue for a matching event without removing the event from the queue, use XPeekIfEvent().