code: function() {
  		if (this._bindingState.child === false && this._childToParent === true) {
  			var options = this._options;
  			this._bindingState.child = true;
  			turnOnListeningAndUpdate(options.child, options.parent, this._updateParent, options.queue);
  		}
  	}
docs: Listen for changes to the child observable and update the parent