Trivial 1. Line 519. Section 3.1.2 should start by saying that the Variable Header for CONNECT consists of four fields. In the order in which they appear, they are Protocol Name, Protocol Version, Connect Flags, and Keep alive timer.
2. Line 541. "The connect flags indicate the presence or absence of fields in the payload and QoS of any Will Message". There are several problems with this sentence
Replace with "The Connect Flags byte contains a number of parameters specifying the behavior of the MQTT connection. It also indicates the presence or absence of fields in the payload."
3. Lines 565 and 588 Qos -> QoS
4. Line 568 clients -> client
5. Line 585 has normative word SHOULD in a non-normative comment. I would suggest saying "..will not receive old publications and has to subscribe afresh to any topics that it is interested in each time it connects"
6. Line 587 "achieves reliable messages" doesn't sound like good English. Replace the sentence with something like "For reliable messaging, use QoS=1 or QoS=2 with cleanSession=0".
7. Line 607. "The value of Will QoS is 0..." -> "The value of Will QoS can be 0.."
8. Line 613 "WillRetain" -> "Will Retain"
9. Lines 615..617 describe the meaning of Will Retain. T
The old words in 3.1 were
"The Will Retain flag indicates whether the server should retain the Will message which is published by the server on behalf of the client in the event that the client is disconnected unexpectedly." which seem reasonably clear to me
The words in WD04 are
"If 0, any will message published by the server on behalf of the client MUST NOT be a retained publication.
"If 1, any will message published by the server on behalf of the client MUST be a retained publication.
I think the MUST be reads strangely.
I guess the reason for rewording was to avoid duplicating the definition of Retain. If so I would prefer
"If 1, the server MUST publish any will message on behalf of the client as a retained publication."
"If 1, the server MUST publish any will message on behalf of the client as a non-retained publication."
To be pedantic you then need to define the terms retained and non-retained in section 2.1.2.3
10. Line 656. "should" -> "SHOULD"