The area put forward for certification has to be a space that can be closed off completely by its walls, floors, ceilings, doors and windows. Walls, ceilings and doors may be made partly or wholly of transparent material. Every door and window must be capable of being locked, or of being secured in some other way. The note explains that these surfaces, transparent sections included, are the containment barrier protecting everything outside the facility, including other spaces inside the building that houses it, and the environment.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.