My understanding is that JSON schema is a bit dormant right now. Not dead, but floundered a bit in the IETF process.
I previously tried to keep my parser up with the latest drafts of the JSON schema spec.
- draft-zyp-json-schema-02 (draft02) was published in early 2010
- draft-zyp-json-schema-03 (draft03) was published in late 2010, and broke backwards compatibility with draft 02 in pretty substantial ways
- draft-zyp-json-schema-04 (draft04) was published in early 2013. draft04 expanded to include draft-fge-json-schema-validation-00 and draft-luff-json-hyper-schema-00. IIRC, hyperschema requires support arbitrary recursive inclusion from remote resources.
None of the JSON schema currently specs seem to be on a track toward getting through an IETF working group and getting published as a Proposed Standard or an Informational RFC. Since it's listed as "Intended status: Informational", that suggests that it hasn't been through the level of scrutiny that Proposed Standards go through. See IETF RFC 1796 ("Not All RFCs are Standards"). A particular note from that document: "The RFC series includes some documents which are informational by nature and other documents which describe experiences. A problem of perception occurs when such a document "looks like" an official protocol specification. Misguided vendors may claim conformance to it, and misguided clients may actually believe that they are buying an Internet standard."
Getting through the IETF publication process is not a requirement for a document to be useful. In fact, it's neat that there are live upstream implementations.
Now that there are two other viable PHP implementations of the Zyp drafts for our use (let alone whatever other language implementations there are), this seems ripe for reevaluation. I'd caution against racing to draft04, though; it's just a draft, and there's no guarantee that Kris Zyp won't publish draft05 completely breaking backwards compatibility with whatever draft04 implementation we migrate to.
Before making a draft03->draft04 migration, I'd prefer we figure out what the upstream's stability strategy is for the specification. Are they still attempting IETF publication? Are they going someplace else like W3C, WHAT-WG, OASIS, or indeieweb.org? Are they attempting to create a new consortium around json-schema.org?
If the upstream specification is stable and trusted, great! If not, then the fallback is having trust that the upstream implementation has a good format stability strategy. We don't want to move to draft04, then have upstream make big changes for draft05, then abandoning us to maintain our own draft04 implementation if we can't migrate with them.