Word description Returns an identifier uniquely representing the game controller device represented by controller. This identifier paired with the device's product-id provides a unique identifier for a particular device that persists between reboots (but not necessarily between computers). This unique identifier can be used to find the same device again with the find-controller-instance word. Depending on the platform, the instance-id may change if the device is plugged into a different port. The type of the identifier value is platform-specific, but equivalent instance-ids are guaranteed to be testable with the = word.