At 4.10.1 and 4.10.2, for example, you say:

4.10.1 Basic Request Response (non-normative)

4.10.2 Determining a Response Topic value (non-normative)

But at Chapter 5:

*****
5 Security
5.1 Introduction
This chapter is provided for guidance only and is non-normative. However, it is strongly recommended that Server implementations that offer TLS [RFC5246] should use TCP port 8883 (IANA service name: secure-mqtt).
*****

I assume that all of 5 is non-normative and so to be consistent, it should read: 5 Security (non-normative)

Then drop the first sentence of 5.1 and revise the second sentence to remove the "however."