Did you know that ISO 8601 is a very large standard that describes more than a single date and time format?
It describes periods, repetitions, many different syntax of describing years, week-of-year, day-of-year, seasons, quarters, semesters, trimesters.
It's mostly unknown because the standards are paywalled: you can't just read ISO 8601 without paying ISO money.
Most of the time, when people refer to ISO 8601, they mean the subset that is described in RFC 3339.
@jerub RFC 3339 is stricter than the subset of ISO 8601 that most people talk about, because it is only a datetime format and requires a time zone.
As far as I can tell there is no standard that describes the subset of ISO8601 that people actually care about.
@pganssle @jerub How about EDTF (level 0) by the Library of Congress? https://www.loc.gov/standards/datetime/
