Mondex digicash system

Are there any technical details as to how it works? It is supposedly anonymous, divisible, transferrable, and offline. I've never seen a practical protocol like this. The message said you could put cards in an electronic wallet and transfer money between them. How can you do this, without losing anonymity? Is it possible this system is security through obscurity or observer-based, as opposed to a pure cryptographic protocol? If the security is non-cryptographic, it will probably be hacked eventually.