Advice on transport ports

[mnot]

Applications that use HTTP SHOULD use the default port for the URL scheme in use.

This isn't really necessary. I would instead say that the port number is in the URL and cite Initial URL Discovery for details.

Then explain that if you are bootstrapping from a bare hostname with .well-known, then this should assume the use of the default port for the scheme unless there are very good reasons. In particular, when it comes to using port numbers other than the default, you can note that there are privacy implications (it makes your protocol distinguishable) and deployment implications (some middleboxes might interfere with the operation of your protocol).

(from @martinthomson)

[mnot]

Does anything stop someone from saying "my application looks up the well-known HTTPS url on port nnnn..."?

Should it? (doing wellknownbis now...).