3.3.7 Other Local Events
The client MAY send a set of informational notification messages to the server when the state of the client machine changes in a way relevant to this protocol. The set of notifications that are considered informational is specified in section 3.2.5. Although all information notifications are optional, the client SHOULD monitor sufficient machine state to issue all informational notifications. Each notification is specified in detail in section 2.2.9.
The only special case is MILMSG_HARDWARETIER, which MAY be sent as either an informational notification or as a response notification. If the server issues a MILCMD_PARTITION_REGISTERFORNOTIFICATIONS message, the client MUST send a MILMSG_HARDWARETIER notification whenever the hardware tier changes. If the server issues a MILCMD_CHANNEL_REQUESTTIER message, the client MUST send a MILMSG_HARDWARETIER message as a reply.