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RFC 3339 / INTERNET TIMESTAMPS

Check calendar limits and leap-second context

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Correct punctuation is only the first check. Calendar days, clock ranges and leap-second events constrain which field values make sense.

DIAGRAMRead RFC section 5.7 ↗
RFC 3339 · § 5.7EXAMPLE
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Check calendar limits and leap-second contextSeparate gates reject April 31, distinguish invalid 1900-02-29 from valid 2000-02-29 using the Gregorian century exception, and reject hour 24 in this profile. The published positive leap insertion runs through 1990-12-31 UTC seconds 59, 60, then 1991-01-01 second 00; 15:59:60-08:00 denotes the same leap instant. The final conditional negative leap goes from 58 to next-minute 00 without asserting a real event. Leap validation needs authoritative event context.Calendar and clock constraints · separate casesConditional negative leap onlyLast second: :58 → next minute :00The second :59 would be absentNo real event is asserted here:58 → next :00Never infer a leap event from a month name alone
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A removed leap second would skip 59.

Conditional example only: if a negative leap second were announced, the last minute would proceed from :58 directly to the next minute’s :00. This is not a claim that such an event occurred.

Source for this drawing: RFC 3339 · Read RFC section 5.7 ↗

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KEY POINT

Validate the calendar and the actual leap context.

  • Day limits depend on month and Gregorian leap year. A year divisible by 4 is a leap year, except centuries must be divisible by 400. The clock hour in this profile is 00–23, even where other ISO forms permit 24.
  • Ordinary seconds run 00–59. An announced inserted leap second permits 60 at the relevant UTC boundary; in another offset it occurs at the same instant with a shifted local clock.
  • A removed leap second would leave 58 as the last second before the next minute. Leap events cannot be predicted far ahead, and applications should not generate inserted-leap timestamps before announcement.
DETAILS

The positive-leap examples are published in §5.8: 1990-12-31T23:59:60Z and 1990-12-31T15:59:60-08:00. The negative-leap illustration is conditional and names no actual event. Appendix D is a historical list, not a current announcement service. The bounded teaching helper handles the published 1990 event separately from ordinary date arithmetic and does not pretend a platform Date parser validates leap seconds.

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