code: public function toStatusLine(): string
      {
          return sprintf("%s %d %s", $this->proto, $this->code, self::getStatus($this->code));
      }
docs: Retrieve the status line
  
  @return string The status line according RFC
  @see http://greenbytes.de/tech/webdav/draft-ietf-httpbis-p1-messaging-latest.html#rfc.section.3.1.2