Section 6.1 forms a request to IANA to register the following WebSocket Indentifier
Subprotocol Identifier mqtt
Subprotocol Common Name mqtt
Subprotocol Definition http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.html

The URL references the MQTT 3.1.1 spec.

Should we simply change the URL in the Subprotocol Definition or do we want to register new names for this version e.g. "mqtt5".

Also, the description of the version name processing for MQTT Connect should probably to include a reference back to MQTT 3.1.1 (i.e., version 4).