Each Operation in PascalCoin (transaction, buy account,..) holds a payload that contains arbitrary data and can be defined when executing an operation.
It can hold values up to 2^8 - 1 bytes or can simply be left empty.
This is a powerful feature often misunderstood or simply not used at all. Exchanges for example use the payload to identify incoming transactions and can associate them with their users. Or an online shop can use the payload to identify a transaction and associate it with an order.
The possibilities are endless, but for now we will stick with explaining how the payload is constructed, what methods to decrypt/encrypt a payload are available and how one can use the JSON RPC API to create transactions with (un)encrypted payloads.