code: function (method, url, async, user, password) {
          var me = this;
          me.method = method;
          me.url = url;
          me.async = async !== false;
          me.user = user;
          me.password = password;
          
          //<debug>
          if (!me.async) {
              Ext.Error.raise("Binary posts are only supported in async mode: " + url);
          }
          if (me.method != "POST") {
              Ext.log.warn("Binary data can only be sent as a POST request: " + url);
          }
          //</debug>
      }
docs: As in XMLHttpRequest.