code: public function url($url = null)
  	{
  		if ($url)
  		{
  			$this->url = $url;
  			$this->option([CURLOPT_URL => $url]);
  		}
  		
  		return $this->url;
  	}
docs: Set or get session url
  
  @param string|null $url if set update session url
  
  @return string