Drivers
Drivers are methods by which values are allocated. You can perform an allocation with or without drivers. In an allocation without drivers, you can allocate values to accounts in proportions that you specify. Use drivers to perform more complex allocations such as allocations by head count or by machine hours etc. You can use different drivers for each step and can use a mixture of driver and non-driver based steps.
If you use a driver, you must select Driver as the allocation type.