code: protected function fetch($url, $encoding, $depth = 0)
      {
          $http_referer = $this->history->getUrl();        
          if ($http_referer) {
              $this->user_agent->setReferer($http_referer->asString());
          } else {
              $this->user_agent->setReferer(null);
          }
  
          $response = $this->user_agent->fetchResponse($url, $encoding);
          if ($response->isError()) {
              return new SimplePage($response);
          }
  
          return $this->parse($response, $depth);
      }
docs: Fetches a page.
  Jointly recursive with the parse() method as it descends a frameset.
  
  @param string/SimpleUrl $url      Target to fetch.
  @param SimpleEncoding $encoding   GET/POST parameters.
  @param int $depth                 Nested frameset depth protection.
  
  @return SimplePage                Parsed page.