Strong Matcher for ISO 8601 / RFC 3339 Date Times; rejects bad TZ offsets, illegal times (Museum of Bad Data)
Handles many nuanced cases around time zone offsets, leap seconds and leap days.
References:
List of UTC Offsets
RFC 3339, the stricter rules that most systems use in practice
ISO 8601, the widely known name for this format...
Submitted by Philip Flip Kromer (@mrflip) - a year ago