RFC 3339 inputs must include T and either Z or an explicit numeric offset. Offset-less inputs use YYYY-MM-DD HH:mm:ss and the selected UTC, local, or IANA timezone.

Local times skipped by a DST transition are rejected. Times repeated during a DST transition are reported with both possible timestamps rather than silently guessed. Precision is preserved up to nanoseconds; the current browser clock is millisecond-based.