As sibling comment mentioned it includes an XML format definition (which itself is surprisingly restrictive, and sort of idiosyncratic for XML), I also found it

As sibling comment mentioned it includes an XML format definition (which itself is surprisingly restrictive, and sort of idiosyncratic for XML), I also found it odd that blesses only those two formats. But Appendix B does give guidance for use in arbitrary formats/media types. Basically it’s format-agnostic, but it covers the two most common/likely scenarios. IMO that’s sensible enough, but it’s not ideal how much the format-agnostic aspect is deemphasized.