Used by the routines at PlotShape, ChangePictureColour, BrightenAttributes, ShapeIfPresent, DrawPatched, DrawFixedShift, DrawFromOrigin, ResetOrigin, ShapeForObject, HorizontalRun, VerticalRun, DrawVertical, FixedVertical and PaintAttributeRun.

Reads the next record byte. FF ends it. FE reflects the left half of the picture onto the right, FD changes one colour to another in the ink and paper, FC paints a run of attributes, FB brightens the picture, FA mirrors it left to right, and F9 draws another room's record. Any other byte goes to DispatchShape.