Intro the FMC Framework
In many aircraft's avionics suites, an CDU or MCDU (multi control and display unit) is present, giving interactive access to many aircraft systems. Notably the FMS/FMC (flight management system/computer) is one of the most commonly accessed systems, followed by an optional ATSU (air traffic systems unit).
The display of information on those screens is, in the vast majority of cases, done via a grid of characters onto which information is displayed line by line. Due to the similarity in how each implementation renders its screen, a framework exists in the MSFS Avionics SDK to facilitate the creation of CDU screens and associated interactions in Microsoft Flight Simulator. This framework is used, as far as stock are concerned, in the WT21 and the Boeing 787-70/747-8i.
Some knowledge regarding CDU screens and their use in aircraft avionics is assumed in the writing of this section.