code: def AddEventTag(self, event_tag):
      
      self._RaiseIfNotWritable()
  
      event_identifier = event_tag.GetEventIdentifier()
      if not isinstance(event_identifier, identifiers.SQLTableIdentifier):
        raise IOError('Unsupported event identifier type: {0:s}'.format(
            type(event_identifier)))
  
      event_tag.event_row_identifier = event_identifier.row_identifier
  
      self._AddAttributeContainer(self._CONTAINER_TYPE_EVENT_TAG, event_tag)
docs: Adds an event tag.
  
      Args:
        event_tag (EventTag): event tag.
  
      Raises:
        IOError: when the storage file is closed or read-only or
            if the event identifier type is not supported.
        OSError: when the storage file is closed or read-only or
            if the event identifier type is not supported.