KembaraXtra – Travel Terms: add-on fare
​ Fares used to build through international fares to/from points not otherwise published in airline tariffs, and also the concept of an amount added to a base fare (for example a “domestic add-on”). The entry explains that once calculated, such fares are treated like published fares, including deriving maximum permitted mileage using mileage add-ons; where tariff rules allow mileage construction, the lowest combination principle applies.