code: public function addByHttpCode(int $code): self
      {
          $serverProtocol = filter_input(
              \INPUT_SERVER,
              'SERVER_PROTOCOL',
              \FILTER_SANITIZE_STRING
          );
          $protocol = !empty($serverProtocol) ? $serverProtocol : 'HTTP/1.1';
          $sHeader   = "{$protocol} {$code} ".self::getHTTPExplanationByCode($code);
          return $this->add($sHeader);
      }
docs: It adds the header to the stack by HTTP code.
  @param integer $code The code.
  @return self.