An input_device describes the device that generated an event (see
event<-device).
Events from the mouse refer to @mouse_device and keyboard
events to @keyboard_device. Pens, touch screens and
gamepads are represented by their own input_device, which is created
when the window system reports the device. The same physical device is
always represented by the same object. display<-input_devices
lists the known devices.
Applications normally only inspect devices, e.g.,
to distinguish pen input from mouse input:
get(@event, device, Device), get(Device, kind, pen)
Devices that can be polled have their own subclass: @keyboard_device is a keyboard and gamepads are of class gamepad.
<-kind.
<-input_devices.