We use state machines
The main concepts of the Defacto API rely on well-defined state-machines.
Therefore, each concept has a set a possible statuses and, for each status, a given set of available transition. Some of which are available to you, and others are managed by Defacto.
All the transitions that you can invoke are prefixed with TO, such as TO_VALIDATE that is available on Loan.
The concepts that are managed by a state machine are the following. Follow their link to discover their state machine.