The id that links a request with its responses, it is up to the calling client to make sure it is unique. However, the client does not have to pass the id if it does not need to link the request with its response. The id is always undefined if the message is unprompted (e.g., with hello) or the id unknown.
The lineage of the given criterion. With this being the representation of a set, there is no guarantee about order.
The at this time unknown type
If you send a message it must not contain a newline but the message must be terminated by a newline.