public function head($url) {
    if(!$this->db) {
      throw new SagException('No database specified');
    }

    //The first char of the URL should be a slash.
    if(strpos($url, '/') !== 0) {
      $url = "/$url";
    }

    if($this->staleDefault) {
      $url = self::setURLParameter($url, 'stale', 'ok');
    }

    //we're only asking for the HEAD so no caching is needed
    return $this->procPacket('HEAD', "/{$this->db}$url");
  }