an Entity references as follows:
An overlay keyboard or concept keyboard is a specialized keyboard with no preset keys. Each key can be programmed with a wide range of different functions. Overlay keyboards are often used as a quick and easy way to input items with just two buttons. Overlay keyboards generally consist of a flat grid of unmarked buttons. A sheet called an overlay is placed on the keyboard to identify each key, after the keyboard is programmed. The overlay can consist of any combination of words, symbols, or pictures.