docs: def validate_one_of(values):
      """
      Validate that a field is in one of the given values.
  
      :param values: Iterable of valid values.
      :raises: ``ValidationError('one_of')``
      """
      def one_of_validator(field, data):
          if field.value is None:
              return
          options = values
          if callable(options):
              options = options()
          if field.value not in options:
              raise ValidationError('one_of', choices=', '.join(map(str, options)))
      return one_of_validator