If you want the big toes of a character to have thumb-like movement, map the toe bones to the LeftFootThumb and RightFootThumb slots of the Mapping List. You might want this behavior if, for example, you have a quadruped with opposable thumbs on their feet, you should use the thumb. You can also use the thumb for dew claws.
If you want the big toes of character to have normal toe movement, map the toe bones to the LeftFootExtraFinger and RightFootExtraFinger slots in the Mapping List.
When you map and characterize this model, the toes use thumb-like behavior unless you rename them or manually map them to the LeftFootExtraFinger or RightFootExtraFinger slots.