The IAB has published RFC 7749: The “xml2rfc” Version 2 Vocabulary.
Abstract: This document defines the “xml2rfc” version 2 vocabulary: an XML-based language used for writing RFCs and Internet-Drafts. Version 2 represents the state of the vocabulary (as implemented by several tools and as used by the RFC Editor) around 2014. This document obsoletes RFC 2629.