code: public function SendHeaders()
      {
          // headers have already been sent
          if (headers_sent()) {
              return $this;
          }
  
          header('HTTP/'.$this->Version.' '.$this->StatusCode.' '.$this->StatusText, true, $this->StatusCode);
  
          foreach ($this->Headers->GetCookies() as $cookie) {
          }
  
          return $this;
      }
docs: Sends HTTP headers.
  
  @return $this