Slab is defined as:
2000-2999 - Get A item @ X price
3000-3999 - Get B item @ Y price
> 4000 - Get C item @ Z price
In a slab wise Bill level promo, user want option to select the level of benefits.
For eg- Bill value Rs.7300/-, in that case default benefit in last slab will be available for the customer. But if customer wants they can avail the benefit of lower slabs even. Further user can also opt for multiple benefits from lower slab if the total bill amount covers it. (Like in above case, user can get 2000-2999 benefit * 2)