public function mung(array $list)
    {
        foreach ($list as $value) {
            if (false === in_array($value, self::$allowedMung)) {
                throw InvalidArgumentException::create(
                    'The $_SERVER variable "%s" is not allowed.',
                    $value
                );
            }
        }

        $this->mung = $list;

        return $this;
    }