I'm building a RESTful web service, and I'm creating some custom media types. It seems like in media types the subtype becomes more specific as you go right to left using '+'. So for example:
application/json is more general than application/hal+json, since HAL adds more restrictions on top of json.
My question is whether this is standard, or just a convention (I've poked through some of the RFCs on MIME types and I couldn't find anything, but I may not have looked hard enough).
If it is standard, does it generalize so I can add even more specific subtypes like application/vnd.custom.mime+hal+json or is it limited to one "+"?