[WorldMaker]

The "dual" standard RFC 8259 [1] (both are normative standards under their respective bodies, ECMA and IETF) is also a useful comparison here. It's wording is a bit stronger than ECMA's, though not by much. ("Good interoperability" is its specific call out.)

It's also interesting that the proposed JSON 5 (standalone) specification [2] doesn't seem to address it at all (but does add back in the other IEEE 754 numbers that ECMA 404 and RFC 8259 exclude from JSON; +/-Infinity and +/-NaN). It both maintains that its numbers are "arbitrary precision" but also requires these few IEEE 754 features, which may be even more confusing than either ECMA 404 or RFC 8259.

[1] https://datatracker.ietf.org/doc/html/rfc8259#section-6

[2] https://spec.json5.org/#numbers