public static function decimal($input, $places = 2) {
        if (!$places) {
            $regex = '/^[-+]?[0-9]*\.{1}[0-9]+(?:[eE][-+]?[0-9]+)?$/';
        } else {
            $regex = '/^[-+]?[0-9]*\.{1}[0-9]{' . $places . '}$/';
        }

        return static::custom($input, $regex);
    }