protected function _parseRange($value)
    {
        $range = parent::_parseRange($value);
        $lower = $this->_normalize($range['lower']);
        $upper = $this->_normalize($range['upper']);
        if (strtotime($lower) > strtotime($upper)) {
            list($lower, $upper) = [$upper, $lower];
        }

        return [
            'lower' => $lower,
            'upper' => $upper,
        ];
    }