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. 255 ends it. 254 reflects the left half of the picture onto the right, 253 changes one colour to another in the ink and paper, 252 paints a run of attributes, 251 brightens the picture, 250 mirrors it left to right, and 249 draws another room's record. Any other byte goes to DispatchShape.