code: function Subscription(name, topic) {
              this._pattern = "%s://%s.mns.%s.aliyuncs.com/topics/%s/subscriptions/%s";
              this._name = name;
              this._topic = topic;
              // make url
              this._urlAttr = this.makeAttrURL();
              // create the OpenStack object
              this._openStack = new AliMNS.OpenStack(topic.getAccount());
          }
docs: The constructor. name & topic is required.