InterUnit-UI presents a user-interface as a sequence of temporal "interface-units".
Each InterUnit presents an interface behavior to service a specific user-goal.
It has full access to the screen and all user-input peripherals.
InterUnits can be independently optimized to achieve ergonomic-efficiency.
A special InterUnit called the EngagementManager interfaces with the underlying OS's display and input peripheral access system.
It serves as a front-end controller for all other InterUnits.
It loads and unloads other InterUnits and manages the current engagement session with the user.
It also maintains some history of app usage.