rear
The cell that is occupied by the item that is closest to the origin of the conveyor that the item is currently on. Null means that the item is not occupying any cells. An item may occupy 1 or more cells depending on the number of cells that it needs while riding on the conveyor. If the segment has 5 cells (1, 2, 3, 4, 5) and the item needs 2 cells and is occupying cells 2 and 3, then its rear cell is 2.