docs: def generate_error_message(tag, err_uniq, err_appl, err_mult):
      """
      Generate the error message for an object.
      """
      err = []
      if err_uniq:
          err.append('Uniqueness restriction: item type %s' % tag.item_type)
      if err_appl:
          err.append('Applicability restriction: field %s' % tag.field)
      if err_mult:
          err.append('Multiplicity restriction: field %s' % tag.field)
      return err