If you read the link, that just adds the HTML markup to plain text ASCII RFCs (which were deprecated in favour of XML, back in 2013 as per RFC 7994.)
RFC 7990 has more details on the format framework. But for actual guidance on the tools used, you probably want to peruse the "Prepare documents" section of the IETF's tools[0] page, or those at rfc-editor.org[1].
Comments
If you read the link, that just adds the HTML markup to plain text ASCII RFCs (which were deprecated in favour of XML, back in 2013 as per RFC 7994.)
RFC 7990 has more details on the format framework. But for actual guidance on the tools used, you probably want to peruse the "Prepare documents" section of the IETF's tools[0] page, or those at rfc-editor.org[1].
[0]: http://tools.ietf.org/
[1]: https://www.rfc-editor.org/pubprocess/tools/
XML, markdown, asciidoc, Bibtex, nroff, and even Word are covered.