front
The cell that is occupied by the item that is the furthest forward (closest to the end) on the conveyor that the item is currently occupying. 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 conveyor has 5 cells (1, 2, 3, 4, 5) and the item needs 2 cells and is occupying cells 2 and 3, then its front cell is 3.