public function userAgent($useragent) {

		if(false === is_string($useragent)) {
            return trigger_error(sprintf('Argument 1 passed to %s() must be of the type string, "%s" given', __METHOD__, gettype($useragent)), E_USER_ERROR);
        }

		$this -> options[CURLOPT_USERAGENT] = $useragent;

		return $this;
	}