protected function isBetween($key, $value) : bool
    {
        $data = string_split($value, ',');
        $min = (int) $data[0];
        $max = (empty($data[1])) ? PHP_INT_MAX : (int) $data[1];
        $num = $this->param[$key];

        if (!is_numeric($num)) {
            $this->errors[$key.self::ERROR] = $this->convertToFieldName($key)." must numeric.";
            return false;
        }

        if ($num > $min && $num < $max) {
            return true;
        }

        $this->errors[$key.self::ERROR] = $this->convertToFieldName($key)." must have a length between the given $min and $max.";
        return false;
    }