RFC7749 defines Version 2 of “xml2rfc”, an XML-based format for authoring RFCs. The xml2rfc v2 format is the preferred format for uploading RFCs to the IETF. There is also the newer Version 3 of xml2rfc, but it is not yet supported for IETF RFCs. (The Version 3 XML still looks similar to Version 2 XML, but supports more features, for example, figures in enumerations.)
As far as I can see, there are no good cross-platform editors for xml2rfc that support highlighting, source code formatting, and a preview of the generated files. For markdown, however, all this exists!
mmark is a markdown processor, written in Go, that translates markdown files into xml2rfc (v2 or v3). It adds a special syntax for meta information (such as the status of the RFC) and supports other features, such as including other files, which is particularly handy for long RFCs. Markdown enjoys a good support in many editors, including online editors such as the one provided by GitHub. This makes writing RFCs significantly easier.
Using mmark is straightforward:
./mmark -2 main.md > /tmp/xml-2; xml2rfc --html /tmp/xml-2
For the work on the OAuth 2.0 Security BCP, I split up the source files into
This way, the metadata and the XML for the references, both of which can confuse syntax highlighting in editors, are separated into their own files.
I recommend reading the mmark syntax manual to learn about the features supported by mmark.
If you are interested in starting a new draft using markdown, I recommend taking a look at the draft-dpop repository and using that as the starting point.
Update 2019-03-28: Added link to dpop draft repository.