type < 0 is reserved for future extension including 2-byte type information

What does this mean for interoperability with older Msgpack implementations? Will they interpret the first type byte as a type they don't support and the second type byte as part of the data? Or will the ext format family be extended to include formats with 2-byte types? If it's the former it seems older implementations won't need to do anything differently from how they handle unknown 1-byte types, but if it's the latter they will fail on the unknown message type. I am inclined to assume it's the former, but the text isn't explicit about it.