This document is ready for publication, with two small nits / questions about the content.

## Nits

- In Section 3, the reader is left hanging -- I expected a statement along the lines of 'The media types in this document allow such out of band information to be conveyed.'

- Throughout, the phrase 'is not considered part of this document' is a bit odd -- do you mean 'is not controlled by this document' or similar?