docs: def orify(event, changed_callback):
      '''
      Override ``set`` and ``clear`` methods on event to call specified callback
      function after performing default behaviour.
  
      Parameters
      ----------
  
      '''
      event.changed = changed_callback
      if not hasattr(event, '_set'):
          # `set`/`clear` methods have not been overridden on event yet.
          # Override methods to call `changed_callback` after performing default
          # action.
          event._set = event.set
          event._clear = event.clear
          event.set = lambda: or_set(event)
          event.clear = lambda: or_clear(event)