I'm not sure what the confusion is, the question being explored is, "how do you define a Money type that features the operations we typically expect to perform

I'm not sure what the confusion is, the question being explored is, "how do you define a Money type that features the operations we typically expect to perform and with the results having the expected properties?". He reviews various well-known published designs and their drawbacks, and outlines a design that does not have those drawbacks. > I find most people usually implement "MoneyBag" intuitively first, so it's odd they left that for third? I have not found that at all.