docs: def validate_none_of(values):
      """
      Validate that a field is not in one of the given values.
  
      :param values: Iterable of invalid values.
      :raises: ``ValidationError('none_of')``
      """
      def none_of_validator(field, data):
          options = values
          if callable(options):
              options = options()
          if field.value in options:
              raise ValidationError('none_of', choices=str.join(', ', options))
      return none_of_validator