code: function HandlerChain() {
          var handlers = this._handlers = [];
          //`handlerChain.handlers` is a promised for the handlers that will be
          //resolved in the nextTick, to give the user time to call `addHandler`.
          this.handlers = new Promise(function(resolve) {
              //Give the user time to register some handlers
              process.nextTick(function() {
                  resolve(handlers);
              });
          });
      }
docs: The `HandlerChain` constructor returns an object with an `addHandler` method. This can be called in chain several times to register handlers.