docs: def validate_range(low=None, high=None):
      """
      Validate the range of a field with either low, high, or equal.
      Should work with anything that supports '>' and '<' operators.
  
      :param low: Smallest value required.
      :param high: Longest value required.
      :raises: ``ValidationError('range_low')``
      :raises: ``ValidationError('range_high')``
      :raises: ``ValidationError('range_between')``
      """
      def range_validator(field, data):
          if field.value is None:
              return
          if low is not None and field.value < low:
              key = 'range_low' if high is None else 'range_between'
              raise ValidationError(key, low=low, high=high)
          if high is not None and field.value > high:
              key = 'range_high' if high is None else 'range_between'
              raise ValidationError(key, low=low, high=high)
      return range_validator