code: public function setHost($host)
      {
          if ($host = $this->truncateHost($host)) {
              $this->host = $host;
  
              return true;
          }
  
          return false;
      }
docs: Sets the host. The cookie rules determine that
  the first two parts are taken for certain TLDs and three for others.
  If the new host does not match these rules then the call will fail.
  
  @param string $host New hostname.
  
  @return bool True if hostname is valid.