code: public function respond()
      {
          if (is_null($this->preparedResponse)) {
              $this->prepareResponse();
          }
  
          if ($this->status instanceof Status) {
              header($this->status->getHttpHeader());
          }
  
          header("Content-Type: {$this->writer->getContentType()}");
          echo $this->preparedResponse;
  
          return $this;
      }
docs: Send the response.
  
  This method sends headers and writes the data to the output stream.
  
  If the response has not yet been prepared, this method will prepare it
  first. This method should be the last thing that happens before the
  script ends.
  
  @return $this