I'm not sure why this text below is separated out in a comment. It seems important to document the "default" value of Receive Maximum.
1083 Non normative comment
1084 Not setting the Receive Maximum value has the same effect as setting it to 65535.
It's also awkwardly phrased. Why not include a reference in the main text:
If Receive Maximum is absent, then its value defaults to 65535.
In a similar section in CONNACK:
1363 If the Receive Maximum value is absent it is the same as setting it to 65535 and the Server MUST NOT
1364 close the network connection because it has received too many unacknowledged PUBLISH packets.