I assume they chose -00:00 because ISO 8601 forbids it, so there isn't an issue of a compliant ISO 8601 stamp having a different meaning under the RFC. Does an

I assume they chose -00:00 because ISO 8601 forbids it, so there isn't an issue of a compliant ISO 8601 stamp having a different meaning under the RFC. Does anything in practice care about + vs. - 00:00, though? Seems kind of unlikely to be widespread. Among other reasons because people don't know about it. I think if anything I'd have just left the concept out entirely.