Only one discount code can be successfully applied per item in Cart. If a donor tries to apply more than one discount code to a single item, Cart will automatically assign the discount code that offers the best value. Once both discount codes have been "applied," the following notification will display next to the lesser-valued discount: "the code was accepted but a better discount is already applied."
The discount codes are not capable of being "stacked" or added together for an aggregate discount - donors may use only one discount code per item.
For example, if a donor enters two discount codes for Item A (one for $10 off and the other for $20 off), Cart will only take $20 off that item - it will not discount that item by a sum of the two discounts added together.