docs: def exec_event_handler(self, event, transactional=False):
          """Execute the Async set to be run on event."""
          # QUESTION: Should we raise an exception if `event` is not in some
          # known event-type list?
  
          callbacks = self._options.get('callbacks', {})
  
          handler = callbacks.get(event)
  
          if not handler:
              raise Exception('Handler not defined!!!')
  
          handler.start(transactional=transactional)