Event code identifying the key or button that triggered the event. These codes are defined by the I/O interface that send them.
ID for the I/O interface representing the input device. The I/O interface defines a code for each event it may send. This means the I/O ID along with the event code should uniquely identify events.
Uniquely codes a pressed key, button or a gesture, by using an I/O ID and event code map. Each I/O interface can define its own keys and buttons it needs to map. The way it maps codes to buttons is left up to the interface to define, but it usually is with an enum.