True when an epoch string pins down an exact instant on its own — a Z/±hh:mm offset, or a bare ISO date (which ISO 8601 defines as UTC). False for a date-time with no offset (see parseEpochMs).
Z
±hh:mm
True when an epoch string pins down an exact instant on its own — a
Z/±hh:mmoffset, or a bare ISO date (which ISO 8601 defines as UTC). False for a date-time with no offset (see parseEpochMs).