Every client of a Parcel must call these methods in a precise sequence drawn via type annotations and receiver parameters. In other words, an order can be placed only if it is a new order, it can be shipped only if the order was placed, it can be delivered only if it was shipped, it can be paid only if it was delivered, and it can be closed only if it was paid.At this moment, this strict sequence is pointed out only by these hypothetical annotations. But, this is the right road to implement further a static analysis tool that will understand the meaning of these annotations and trigger warnings every time a client of Parcel doesn’t follow this precise sequence.