Minor In 3.1.2.3.2. there's a normative statement "
The Will Flag indicates that a Will Message MUST be published by the server when the server detects that the client is disconnected for any reason other than the client flowing a DISCONNECT Packet [MQTT-3.1.2-7]"
1. Editorial comment - This should say "If the Will Flag is set to 1, a Will Message MUST be published by the server when the server detects that the client is disconnected for any reason other than the client flowing a DISCONNECT Packet [MQTT-3.1.2-7]"
2. Core comment. For the avoidance of doubt, we should say what happens if the Will Flag is 0
I assume that the default is that no will message gets published, but if a server wants to use a $SYS topic to log unexpected disconnects, then it is free to do that, We should consider making it clear that a server does not "remember" the last Will Mesage / Topic that the client used.