code: def GetMessages(self, formatter_mediator, event):
      
      if self.DATA_TYPE != event.data_type:
        raise errors.WrongFormatter('Unsupported data type: {0:s}.'.format(
            event.data_type))
  
      event_values = event.CopyToDict()
  
      visit_type = event_values.get('visit_type', 0)
      transition = self._URL_TRANSITIONS.get(visit_type, None)
      if transition:
        transition_str = 'Transition: {0!s}'.format(transition)
  
      extra = event_values.get('extra', None)
      if extra:
        if transition:
          extra.append(transition_str)
        event_values['extra_string'] = ' '.join(extra)
  
      elif transition:
        event_values['extra_string'] = transition_str
  
      return self._ConditionalFormatMessages(event_values)
docs: Determines the formatted message strings for an event object.
  
      Args:
        formatter_mediator (FormatterMediator): mediates the interactions
            between formatters and other components, such as storage and Windows
            EventLog resources.
        event (EventObject): event.
  
      Returns:
        tuple(str, str): formatted message string and short message string.
  
      Raises:
        WrongFormatter: if the event object cannot be formatted by the formatter.