JSON and IETF JSON feel different in spirit in some important ways to me.
For example, numbers.
JSON doesn't seem to put constraints on numbers. JSON also doesn't seem to suggest that decoding numbers in a lossy way is acceptable
IETF JSON suggests a constraint and even a lossy-ness on numbers that has been included some JSON implementations
I would have preferred that the paragraph in the screen-shot, from the latest IETF RFC, did not exist in there