1. A method comprising: by a computing device, receiving user input comprising a two-dimensional pinch event during execution of an application executing on the computing device, the application comprising one or more user-interface layers in a navigation hierarchy; by the computing device, determining a user-interface layer of the application corresponding to the pinch event; and by the computing device: if the user-interface layer of the application corresponding to the pinch event is a root layer of the navigation hierarchy, then terminating presentation of the application on the computing device; or if the user-interface layer of the application corresponding to the pinch event is not the root layer of the navigation hierarchy, then closing the user-interface layer of the application corresponding to the pinch event and navigating to a parent user-interface layer of the user-interface layer of the application corresponding to the pinch event.