path: root/doc/rfc/rfc9636.txt

Internet Engineering Task Force (IETF)                          A. Olson
Request for Comments: 9636                                              
Obsoletes: 8536                                                P. Eggert
Category: Standards Track                                           UCLA
ISSN: 2070-1721                                             K. Murchison
                                                                Fastmail
                                                            October 2024


                The Time Zone Information Format (TZif)

Abstract

   This document specifies the Time Zone Information Format (TZif) for
   representing and exchanging time zone information, independent of any
   particular service or protocol.  Two media types for this format are
   also defined.

   This document replaces and obsoletes RFC 8536.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9636.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Conventions Used in This Document
   3.  The Time Zone Information Format (TZif)
     3.1.  TZif Header
     3.2.  TZif Data Block
     3.3.  TZif Footer
       3.3.1.  All-Year Daylight Saving Time
       3.3.2.  TZ String Extension
   4.  Interoperability Considerations
   5.  Internationalization Considerations
   6.  Use with the Time Zone Data Distribution Service
     6.1.  Truncating TZif Files
     6.2.  Example TZDIST Request for TZif Data
   7.  Security Considerations
   8.  Privacy Considerations
   9.  IANA Considerations
     9.1.  application/tzif
     9.2.  application/tzif-leap
   10. References
     10.1.  Normative References
     10.2.  Informative References
   Appendix A.  Common Interoperability Issues
   Appendix B.  Example TZif Files
     B.1.  Version 1 File Representing UTC (with Leap Seconds)
     B.2.  Version 2 File Representing Pacific/Honolulu
     B.3.  Truncated Version 2 File Representing Pacific/Johnston
     B.4.  Truncated Version 3 File Representing Asia/Jerusalem
     B.5.  Truncated Version 4 File Representing Europe/London
   Appendix C.  Changes from RFC 8536
   Acknowledgments
   Authors' Addresses

1.  Introduction

   Time zone data typically consists of offsets from universal time
   (UT), daylight saving transition rules, one or more local time
   designations (acronyms or abbreviations), and optional leap-second
   adjustments.  One such format for conveying this information is
   iCalendar [RFC5545].  It is a text-based format used by calendaring
   and scheduling systems.

   This document specifies the widely deployed Time Zone Information
   Format (TZif).  It is a binary format used by most UNIX systems to
   calculate local time.  This format was introduced in the 1980s and
   has evolved since then into multiple upward-compatible versions.
   There is a wide variety of interoperable software capable of
   generating and reading files in this format [tz-link].

   This specification does not define the source of the data assembled
   into a TZif file.  One such source is the IANA-hosted time zone
   database [RFC6557].

   This document obsoletes [RFC8536], providing editorial improvements,
   new details, and errata fixes while keeping full compatibility with
   the interchange format of [RFC8536].  Additionally, a new version of
   the format is defined.  The changes from [RFC8536] are summarized in
   Appendix C.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The following terms are used in this document (see "Time zone and
   daylight saving time data" [tz-link] for more detailed information
   about civil timekeeping data and practice):

   Coordinated Universal Time (UTC):  The basis for civil time since
      1960.  It is approximately equal to mean solar time at the prime
      meridian (0 degrees longitude).

   Daylight Saving Time (DST):  The time according to a location's law
      or practice, when adjusted as necessary from standard time.  The
      adjustment may be positive or negative, and the amount of
      adjustment may vary depending on the date and time; the TZif
      format even allows the adjustment to be zero, although this is not
      common practice.

   International Atomic Time (TAI):  The time standard based on atomic
      clocks since 1972.  It is equal to UTC but without leap-second
      adjustments.

   Leap Second:  A one-second adjustment to keep UTC close to mean solar
      time at the prime meridian (see [ITU-R-TF.460]).  Each inserted or
      deleted leap second occurs at the end of a UTC month, that is, a
      month using the Gregorian calendar and the UTC timescale.

   Leap-Second Correction (LEAPCORR):  The value of "TAI - UTC - 10" for
      timestamps after the first leap second, and zero for timestamps
      before that.  The expression "TAI - UTC - 10" comes from the fact
      that TAI - UTC was defined to be 10 just prior to the first leap
      second in 1972, so clocks with leap seconds have a zero LEAPCORR
      before the first leap second.

   Local Time:  Civil time for a particular location.  Its offset from
      universal time can depend on the date and time of day.

   POSIX Epoch:  1970-01-01 00:00:00 UTC, the basis for absolute
      timestamps in this document.

   Standard Time:  The time according to a location's law or practice,
      unadjusted for daylight saving time.

   Time Change:  A change to civil timekeeping practice.  It occurs when
      one or more of the following happen simultaneously:

      1.  a change in UT offset

      2.  a change in whether daylight saving time is in effect

      3.  a change in time zone abbreviation

      4.  a leap second (i.e., a change in LEAPCORR)

   Time Zone Data:  The Time Zone Data Distribution Service (TZDIST)
      [RFC7808] defines "Time zone data" as "data that defines a single
      time zone, including an identifier, UTC offset values, DST rules,
      and other information such as time zone abbreviations".  The
      interchange format defined in this document is one such form of
      time zone data.

   Transition Time:  The moment of occurrence of a time change that is
      not a leap second.  It is identified with a signed integer count
      of UNIX leap time seconds since the POSIX epoch.

   Universal Time (UT):  The basis of civil time.  This is the principal
      form of the mean solar time at the prime meridian (0 degrees
      longitude) for timestamps before UTC was introduced in 1960 and is
      UTC for timestamps thereafter.  Although UT is sometimes called
      "UTC" or "GMT" in other sources, this specification uses the term
      "UT" to avoid confusion with UTC or with GMT.

   UNIX Time:  The time as returned by the time() function provided by
      the C programming language (see Section 3 of the "System
      Interfaces" volume of [POSIX]).  This is an integer number of
      seconds since the POSIX epoch, not counting leap seconds.  As an
      extension to POSIX, negative values represent times before the
      POSIX epoch, using UT.

   UNIX Leap Time:  UNIX time plus all preceding leap-second
      corrections.  For example, if the first leap-second record in a
      TZif file occurs at 1972-06-30 23:59:60 UTC, the UNIX leap time
      for the timestamp 1972-07-01 00:00:00 UTC would be 78796801, one
      greater than the UNIX time for the same timestamp.  Similarly, if
      the second leap-second record occurs at 1972-12-31 23:59:60 UTC,
      it accounts for the first leap second, so the UNIX leap time of
      1972-12-31 23:59:60 UTC would be 94694401, and the UNIX leap time
      of 1973-01-01 00:00:00 UTC would be 94694402.  If a TZif file
      specifies no leap-second records, UNIX leap time is equal to UNIX
      time.

   Wall Time:  Another name for local time; short for "wall-clock time".

3.  The Time Zone Information Format (TZif)

   The Time Zone Information Format begins with a fixed 44-octet version
   1 header (Section 3.1) containing a field that specifies the version
   of the file's format.  Readers designed for version N can read
   version N+1 files without too much trouble; data specific to version
   N+1 either appears after version N data so that earlier version
   readers can easily ignore later version data they are not designed
   for, or it appears as a minor extension to version N that version N
   readers are likely to tolerate well.

   The version 1 header is followed by a variable-length version 1 data
   block (Section 3.2) containing four-octet (32-bit) transition times
   and leap-second occurrences.  These 32-bit values are limited to
   representing time changes from 1901-12-13 20:45:52 through 2038-01-19
   03:14:07 UT, and the version 1 header and data block are present only
   for backward compatibility with obsolescent readers, as discussed in
   "Common Interoperability Issues" (Appendix A).

   Version 1 files terminate after the version 1 data block.  Files from
   versions 2 and higher extend the format by appending a second
   44-octet version 2+ header, a variable-length version 2+ data block
   containing eight-octet (64-bit) transition times and leap-second
   occurrences, and a variable-length footer (Section 3.3).  These
   64-bit values can represent times approximately 292 billion years
   into the past or future.

   NOTE: All multi-octet integer values MUST be stored in network octet
   order format (high-order octet first, otherwise known as big-endian),
   with all bits significant.  Signed integer values MUST be represented
   using two's complement.

   A TZif file is structured as follows:

                        Version 1        Versions 2+
                     +-------------+   +-------------+
                     |  Version 1  |   |  Version 1  |
                     |   Header    |   |   Header    |
                     +-------------+   +-------------+
                     |  Version 1  |   |  Version 1  |
                     |  Data Block |   |  Data Block |
                     +-------------+   +-------------+
                                       |  Version 2+ |
                                       |   Header    |
                                       +-------------+
                                       |  Version 2+ |
                                       |  Data Block |
                                       +-------------+
                                       |   Footer    |
                                       +-------------+

                   Figure 1: General Format of TZif Files

3.1.  TZif Header

   A TZif header is structured as follows (the lengths of multi-octet
   fields are shown in parentheses):

       +---------------+---+
       |  magic    (4) |ver|
       +---------------+---+---------------------------------------+
       |           [unused - reserved for future use] (15)         |
       +---------------+---------------+---------------+-----------+
       |  isutcnt  (4) |  isstdcnt (4) |  leapcnt  (4) |
       +---------------+---------------+---------------+
       |  timecnt  (4) |  typecnt  (4) |  charcnt  (4) |
       +---------------+---------------+---------------+

                           Figure 2: TZif Header

   The fields of the header are defined as follows:

   magic:  The four-octet ASCII [RFC20] sequence "TZif" (0x54 0x5A 0x69
      0x66), which identifies the file as utilizing the Time Zone
      Information Format.

   ver(sion):  An octet identifying the version of the file's format.
      The value MUST be one of the following:

      *  NUL (0x00) Version 1 - The file contains only the version 1
         header and data block.  Version 1 files MUST NOT contain a
         version 2+ header, data block, or footer.

      *  '2' (0x32) Version 2 - The file MUST contain the version 1
         header and data block, a version 2+ header and data block, and
         a footer.  The TZ string in the footer (Section 3.3), if non-
         empty, MUST strictly adhere to the requirements for the TZ
         environment variable as defined in Section 8.3 of the "Base
         Definitions" volume of [POSIX] and MUST encode the POSIX
         portable character set as ASCII.  The leap-second records MUST
         NOT be truncated at the start (Section 6.1) and MUST NOT
         contain an expiration time.

      *  '3' (0x33) Version 3 - The file MUST conform to all version 2
         requirements, except that any TZ string in the footer
         (Section 3.3) MAY use the TZ string extension described below
         (Section 3.3.2).

      *  '4' (0x34) Version 4 - The file MUST conform to all version 3
         requirements, except that the leap-second records MAY be
         truncated at the start and MAY contain an expiration time.

   isutcnt:  A four-octet unsigned integer specifying the number of UT/
      local indicators contained in the data block -- MUST either be
      zero or equal to "typecnt".

   isstdcnt:  A four-octet unsigned integer specifying the number of
      standard/wall indicators contained in the data block -- MUST
      either be zero or equal to "typecnt".

   leapcnt:  A four-octet unsigned integer specifying the number of
      leap-second records contained in the data block.

   timecnt:  A four-octet unsigned integer specifying the number of
      transition times contained in the data block.

   typecnt:  A four-octet unsigned integer specifying the number of
      local time type records contained in the data block -- MUST NOT be
      zero.  (Although local time type records convey no useful
      information in files that have non-empty TZ strings but no
      transitions, at least one such record is nevertheless required
      because many TZif readers reject files that have zero time types.)

   charcnt:  A four-octet unsigned integer specifying the total number
      of octets used by the set of time zone designations contained in
      the data block -- MUST NOT be zero.  The count includes the
      trailing NUL (0x00) octet at the end of the last time zone
      designation.

   Although the version 1 and 2+ headers have the same format, magic
   number, and version fields, their count fields may differ, because
   the version 1 data can be a subset of the version 2+ data.

3.2.  TZif Data Block

   A TZif data block consists of seven variable-length elements, each of
   which is a series of items.  The number of items in each series is
   determined by the corresponding count field in the header.  The total
   length of each element is calculated by multiplying the number of
   items by the size of each item.  Therefore, implementations that do
   not wish to parse or use the version 1 data block can calculate its
   total length and skip directly to the header of the version 2+ data
   block.

   In the version 1 data block, time values are 32 bits (TIME_SIZE = 4
   octets).  In the version 2+ data block, present only in version 2 and
   higher files, time values are 64 bits (TIME_SIZE = 8 octets).

   The data block is structured as follows (the lengths of multi-octet
   fields are shown in parentheses):

        +---------------------------------------------------------+
        |  transition times          (timecnt x TIME_SIZE)        |
        +---------------------------------------------------------+
        |  transition types          (timecnt)                    |
        +---------------------------------------------------------+
        |  local time type records   (typecnt x 6)                |
        +---------------------------------------------------------+
        |  time zone designations    (charcnt)                    |
        +---------------------------------------------------------+
        |  leap-second records       (leapcnt x (TIME_SIZE + 4))  |
        +---------------------------------------------------------+
        |  standard/wall indicators  (isstdcnt)                   |
        +---------------------------------------------------------+
        |  UT/local indicators       (isutcnt)                    |
        +---------------------------------------------------------+

                         Figure 3: TZif Data Block

   The elements of the data block are defined as follows:

   transition times:  A series of four- or eight-octet UNIX leap time
      values sorted in strictly ascending order.  Each value is used as
      a transition time at which the rules for computing local time may
      change.  The number of time values is specified by the "timecnt"
      field in the header.  Each time value SHOULD be at least -2^59.
      (-2^59 is the greatest negated power of 2 that predates the Big
      Bang, and avoiding earlier timestamps works around known TZif
      reader bugs relating to outlandishly negative timestamps.)

   transition types:  A series of one-octet unsigned integers specifying
      the type of local time of the corresponding transition time.
      These values serve as zero-based indices into the array of local
      time type records.  The number of type indices is specified by the
      "timecnt" field in the header.  Each type index MUST be in the
      range [0, "typecnt" - 1].

   local time type records:  A series of six-octet records specifying a
      local time type.  The number of records is specified by the
      "typecnt" field in the header.  Each record has the following
      format (the lengths of multi-octet fields are shown in
      parentheses):

      +---------------+---+---+
      |  utoff (4)    |dst|idx|
      +---------------+---+---+

      utoff:  A four-octet signed integer specifying the number of
         seconds to be added to UT in order to determine local time.
         The value MUST NOT be -2^31 and SHOULD be in the range [-89999,
         93599] (i.e., its value SHOULD be more than -25 hours and less
         than 26 hours).  Avoiding -2^31 allows 32-bit clients to negate
         the value without overflow.  Restricting it to [-89999, 93599]
         allows easy support by implementations that already support the
         POSIX-required range [-24:59:59, 25:59:59].

      (is)dst:  A one-octet value indicating whether local time should
         be considered Daylight Saving Time (DST).  The value MUST be 0
         or 1.  A value of one (1) indicates that this type of time is
         DST.  A value of zero (0) indicates that this time type is
         standard time.

      (desig)idx:  A one-octet unsigned integer specifying a zero-based
         index into the series of time zone designation octets, thereby
         selecting a particular designation string.  Each index MUST be
         in the range [0, "charcnt" - 1]; it designates the
         NUL-terminated string of octets starting at position "idx" in
         the time zone designations.  (This string MAY be empty.)  A NUL
         octet MUST exist in the time zone designations at or after
         position "idx".  If the designation string is "-00", the time
         type is a placeholder indicating that local time is
         unspecified.

   time zone designations:  A series of octets constituting an array of
      NUL-terminated (0x00) time zone designation strings.  The total
      number of octets is specified by the "charcnt" field in the
      header.  Two designations MAY overlap if one is a suffix of the
      other.  The character encoding of time zone designation strings is
      not specified; however, see Section 4 of this document.

   leap-second records:  A series of eight- or twelve-octet records
      specifying the corrections that need to be applied to UTC in order
      to determine TAI, also known as the leap-second table.  The
      records are sorted by the occurrence time in strictly ascending
      order.  The number of records is specified by the "leapcnt" field
      in the header.  Each record has one of the following structures
      (the lengths of multi-octet fields are shown in parentheses):

      Version 1 Data Block:
         +---------------+---------------+
         |  occur (4)    |  corr (4)     |
         +---------------+---------------+

      version 2+ Data Block:
         +---------------+---------------+---------------+
         |  occur (8)                    |  corr (4)     |
         +---------------+---------------+---------------+

      occur(rence):  A four- or eight-octet UNIX leap time value
         specifying the time at which a leap-second correction occurs or
         at which the leap-second table expires.  The first value, if
         present, MUST be non-negative, and each leap second MUST occur
         at the end of a UTC month.

      corr(ection):  A four-octet signed integer specifying the value of
         LEAPCORR on or after the occurrence.  If "leapcnt" is zero,
         LEAPCORR is zero for all timestamps.  If "leapcnt" is nonzero,
         for timestamps before the first occurrence time, LEAPCORR is
         zero if the first correction is one (1) or minus one (-1) and
         is unspecified otherwise (which can happen only in files
         truncated at the start (Section 6.1)).

         The first leap second is a positive leap second if and only if
         its correction is positive.  Each correction after the first
         MUST differ from the previous correction by either one (1) for
         a positive leap second or minus one (-1) for a negative leap
         second, except that in version 4 files with two or more leap-
         second records, the correction value of the last two records
         MAY be the same, with the occurrence of last record indicating
         the expiration time of the leap-second table.

         The leap-second table expiration time is the time at which the
         table no longer records the presence or absence of future leap-
         second corrections, and post-expiration timestamps cannot be
         accurately calculated.  For example, a leap-second table
         published in January, which predicts the presence or absence of
         a leap second at June's end, might expire in mid-December
         because it is not known when the next leap second will occur.

         If leap seconds become permanently discontinued, as requested
         by the General Conference on Weights and Measures
         [CGPM-2022-R4], leap-second tables published after the
         discontinuation time SHOULD NOT expire, since they will not be
         updated in the foreseeable future.

   standard/wall indicators:  A series of one-octet values indicating
      whether the transition times associated with local time types were
      specified as standard time or wall-clock time.  Each value MUST be
      0 or 1.  A value of one (1) indicates standard time.  The value
      MUST be set to one (1) if the corresponding UT/local indicator is
      set to one (1).  A value of zero (0) indicates wall time.  The
      number of values is specified by the "isstdcnt" field in the
      header.  If "isstdcnt" is zero (0), all transition times
      associated with local time types are assumed to be specified as
      wall time.

   UT/local indicators:  A series of one-octet values indicating whether
      the transition times associated with local time types were
      specified as UT or local time.  Each value MUST be 0 or 1.  A
      value of one (1) indicates UT, and the corresponding standard/wall
      indicator MUST also be set to one (1).  A value of zero (0)
      indicates local time.  The number of values is specified by the
      "isutcnt" field in the header.  If "isutcnt" is zero (0), all
      transition times associated with local time types are assumed to
      be specified as local time.

   The type corresponding to a transition time specifies local time for
   timestamps starting at the given transition time and continuing up
   to, but not including, the next transition time.  Local time for
   timestamps before the first transition is specified by the first time
   type (time type 0).  Local time for timestamps on or after the last
   transition is specified by the TZ string in the footer (Section 3.3)
   if present and non-empty; otherwise, it is unspecified.  If there are
   no transitions, local time for all timestamps is specified by the TZ
   string in the footer if present and non-empty; otherwise, it is
   specified by time type 0.  A time type with a designation string of
   "-00" represents an unspecified local time.

   A given pair of standard/wall and UT/local indicators is used to
   designate whether the corresponding transition time was specified as
   UT, standard time, or wall-clock time.  There are only three
   combinations of the two indicators, given that the standard/wall
   value MUST be one (1) if the UT/local value is one (1).  This
   information can be useful if the transition times in a TZif file need
   to be transformed into transitions appropriate for another time zone
   (e.g., when calculating transition times for a simple POSIX-like TZ
   string such as "AKST9AKDT").

   In order to eliminate unused space in a TZif file, every nonzero
   local time type index SHOULD appear at least once in the transition
   type array.  Likewise, every octet in the time zone designations
   array SHOULD be used by at least one time type record.

3.3.  TZif Footer

   The TZif footer is structured as follows (the lengths of multi-octet
   fields are shown in parentheses):

                      +---+--------------------+---+
                      | NL|  TZ string (0...)  |NL |
                      +---+--------------------+---+

                           Figure 4: TZif Footer

   The elements of the footer are defined as follows:

   NL:  An ASCII new line character (0x0A).

   TZ string:  A rule for computing local time changes after the last
      transition time stored in the version 2+ data block.  The string
      is either empty or uses the expanded format of the "TZ"
      environment variable as defined in Section 8.3 of the "Base
      Definitions" volume of [POSIX] with ASCII encoding, possibly
      utilizing the extension described below (Section 3.3.2) in version
      3 and higher files.  If the string is empty, the corresponding
      information is not available.  If the string is non-empty and one
      or more transitions appear in the version 2+ data, the string MUST
      be consistent with the last version 2+ transition.  In other
      words, evaluating the TZ string at the time of the last transition
      should yield the same time type as was specified in the last
      transition.  The string MUST NOT contain NUL octets or be
      NUL-terminated, and it SHOULD NOT begin with the ":" (colon)
      character.

   The TZif footer is present only in version 2 and higher files, as the
   obsolescent version 1 format was designed before the need for a
   footer was apparent.

3.3.1.  All-Year Daylight Saving Time

   DST is considered to be in effect all year if its UT offset is less
   than (i.e., west of) that of standard time, and it starts January 1
   at 00:00 and ends December 31 at 24:00 minus the difference between
   standard and daylight saving time, leaving no room for standard time
   in the calendar.  [POSIX] implies but does not explicitly state this,
   so it is spelled out here for clarity.

   Example: XXX3EDT4,0/0,J365/23
      This represents a time zone that is perpetually 4 hours west of UT
      and is abbreviated "EDT".  The "XXX" is ignored.

3.3.2.  TZ String Extension

   The TZ string in a version 3 or higher TZif file MAY use the
   following extension to POSIX TZ strings.  This extension is described
   using the terminology of Section 8.3 of the "Base Definitions" volume
   of [POSIX].

   The hours part of the transition times may be signed and range from
   -167 through 167 (-167 <= hh <= 167) instead of the POSIX-required
   unsigned values from 0 through 24.

   Example: <-03>3<-02>,M3.5.0/-2,M10.5.0/-1
      This represents a time zone that observes daylight saving time
      from 22:00 on the day before March's last Sunday until 23:00 on
      the day before October's last Sunday.  Standard time is 3 hours
      west of UT and is abbreviated "-03"; daylight saving time is 2
      hours west of UT and is abbreviated "-02".

   A TZif file that uses the above extension MUST be designated as
   version 3 (or higher), even if a future version of POSIX adopts this
   extension.

4.  Interoperability Considerations

   The following practices help ensure the interoperability of TZif
   applications.

   *  Version 1 files are considered a legacy format and SHOULD NOT be
      generated, as they do not support transition times after the year
      2038.

   *  Readers that understand only version 1 MUST ignore any data that
      extends beyond the calculated end of the version 1 data block.

   *  Other than version 1, writers SHOULD generate the lowest version
      number needed by a file's data.  This helps interoperability with
      older readers.  For example, a writer SHOULD generate a version 4
      file only if its leap-second table either expires or is truncated
      at the start.  Likewise, a writer not generating a version 4 file
      SHOULD generate a version 3 file only if the TZ string extension
      is necessary to accurately model transition times.

   *  To save space, writers of version 2+ files MAY output a
      placeholder version 1 data block with all counts zero except that
      "typecnt" and "charcnt" are both one (1).  If this is done,
      obsolescent version-1-only readers MUST interpret these files as
      lacking time changes and time zone abbreviations.

   *  Unless the version 1 data block is a placeholder, the sequence of
      timestamps defined by the version 1 header and data block SHOULD
      be a contiguous sub-sequence of the timestamps defined by the
      version 2+ header and data block and by the footer.  This
      guideline helps obsolescent version 1 readers agree with current
      readers about timestamps within the contiguous sub-sequence.

   *  When a TZif file contains a leap-second table expiration time,
      TZif readers SHOULD either refuse to process post-expiration
      timestamps or process them as if the expiration time did not exist
      (possibly with an error indication).  This lessens disagreement
      among implementations when processing far-future timestamps that
      cannot yet be handled exactly.

   *  Time zone designations MUST consist of at least three (3) and no
      more than six (6) ASCII characters from the set of alphanumerics,
      "-", and "+".  This is compatible with POSIX requirements for time
      zone abbreviations.

   *  A reader that encounters a time zone designation containing bytes
      other than ASCII alphanumerics, "-", and "+" SHOULD act if the
      designation instead contained a signed numeric string derived from
      the UT offset, for example, "-10" and "+0530" to indicate 10 hours
      west and 5.5 hours east of Greenwich, respectively.

   *  When reading a version 2 or higher file, readers SHOULD ignore the
      version 1 header and data block except for the purpose of skipping
      over them.  This improves compatibility among readers of non-
      conforming files where version 2+ data is not upward compatible
      with version 1.

   *  Readers SHOULD calculate the total lengths of the headers and data
      blocks and check that they all fit within the actual file size, as
      part of a validity check for the file.

   *  When a TZif file is used in a MIME message entity, it SHOULD be
      indicated by one of the following media types:

      -  "application/tzif-leap" (Section 9.2) to indicate that leap-
         second records are included in the TZif data as necessary (none
         are necessary if the file is truncated to a range that precedes
         the first leap second).

      -  "application/tzif" (Section 9.1) to indicate that leap-second
         records are not included in the TZif data; "leapcnt" in the
         header(s) MUST be zero (0).

   *  Common interoperability issues and possible workarounds are
      described in Appendix A.

5.  Internationalization Considerations

   TZif time zone designations contain only ASCII alphanumerics, "-",
   and "+".  Commonly used designations include numeric strings like
   "-10" and "+0530" for UT offsets and English language abbreviations
   like "CEST" for Central European Summer Time and "GMT" for Greenwich
   Mean Time.  It is the TZif reader's responsibility to substitute
   different abbreviations when needed for internationalization, such as
   substituting "HNC" (l'heure normale du Centre) for "CST" (Central
   Standard Time) in French-speaking regions.  This substitution can be
   problematic, as abbreviations can be ambiguous; for example, "CST"
   commonly stands for China Standard Time and Cuba Standard Time as
   well as Central Standard Time.  One approach for addressing this
   issue can be found in the time zone charts of the Unicode Common
   Locale Data Repository (CLDR) Project [CLDR].

   Although the original TZif design allowed for any nonzero octets in
   time zone designations, and it was common practice until the mid-
   1990s for designations to contain ASCII spaces, designations are now
   limited to ASCII alphanumerics, "-", and "+" to avoid confusion and
   to encourage portability to a wide variety of locales.

6.  Use with the Time Zone Data Distribution Service

   The Time Zone Data Distribution Service (TZDIST) [RFC7808] is a
   service that allows reliable, secure, and fast delivery of time zone
   data and leap-second rules to client systems such as calendaring and
   scheduling applications or operating systems.

   A TZDIST service MAY supply time zone data to clients in the Time
   Zone Information Format.  Such a service MUST indicate that it
   supports this format by including the media type "application/tzif"
   (Section 9.1) in its "capabilities" response (Section 5.1 of
   [RFC7808]).  A TZDIST service MAY also include the media type
   "application/tzif-leap" (Section 9.2) in its "capabilities" response
   if it is able to generate TZif files containing leap-second records.
   A TZDIST service MUST NOT advertise the "application/tzif-leap" media
   type without also advertising "application/tzif".

   TZDIST clients MUST use the HTTP "Accept" header field ([RFC9110],
   Section 12.5.1) to indicate their preference to receive data in the
   "application/tzif" and/or "application/tzif-leap" formats.

6.1.  Truncating TZif Files

   As described in Section 3.9 of [RFC7808], a TZDIST service MAY
   truncate time zone transition data.  A truncated TZif file is valid
   from its first and up to, but not including, its last version 2+
   transition time, if present.

   When truncating the start of a TZif file, the service MUST supply in
   the version 2+ data a first transition time that is the start point
   of the truncation range.  As with untruncated TZif files, time type 0
   indicates local time immediately before the start point, and the time
   type of the first transition indicates local time thereafter.  Time
   type 0 MUST be a placeholder indicating that local time is
   unspecified, so that the reader is unambiguously informed of
   truncation at the start.

   When truncating the start of a TZif file containing leap-second
   records, the service MUST keep all leap-second records governing
   timestamps within the truncation range, even if the first such record
   precedes the start point of the truncation range.  If the truncated
   leap-second table is non-empty, its first record MUST have a positive
   correction if and only if it represents a positive leap second.

   When truncating the end of a TZif file, the service MUST supply in
   the version 2+ data a last transition time that is the end point of
   the truncation range and MUST supply an empty TZ string.  As with
   untruncated TZif files with empty TZ strings, a truncated TZif file
   does not indicate local time after the last transition.  To this end,
   the time type of the last transition MUST be a placeholder indicating
   that local time is unspecified.

   All represented information that falls inside the truncation range
   MUST be the same as that represented by a corresponding untruncated
   TZif file.

   TZDIST clients SHOULD NOT use a truncated TZif file (as described
   above) to interpret timestamps outside the truncation time range.

6.2.  Example TZDIST Request for TZif Data

   In this example, the client checks the server for the available
   formats and then requests that the time zone with a specific time
   zone identifier be returned in Time Zone Information Format.

   This example presumes that the time zone context path has been
   discovered (see [RFC7808], Section 4.2.1) to be "/tzdist".

   >> Request <<

   GET /tzdist/capabilities HTTP/1.1
   Host: tz.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Date: Fri, 01 Jun 2018 14:52:23 GMT
   Content-Type: application/json
   Content-Length: xxxx

   {
     "version": 1,

     "info": {
       "primary-source": "IANA:2018e",
       "formats": [
         "text/calendar",
         "application/tzif",
         "application/tzif-leap"
       ],
   ...
     },
   ...
   }


   >> Request <<

   GET /tzdist/zones/America%2FNew_York HTTP/1.1
   Host: tz.example.com
   Accept: application/tzif

   >> Response <<

   HTTP/1.1 200 OK
   Date: Fri, 01 Jun 2018 14:52:24 GMT
   Content-Type: application/tzif
   Content-Length: xxxx
   ETag: "123456789-000-111"

   TZif2...[binary data without leap-second records]...
   EST5EDT,M3.2.0,M11.1.0

7.  Security Considerations

   The Time Zone Information Format contains no executable code, and it
   does not define any extensible areas that could be used to store such
   code.

   TZif contains counted arrays of data elements.  All counts should be
   checked when processing TZif objects, to guard against references
   past the end of the object.

   TZif provides no confidentiality or integrity protection.  Time zone
   information is normally public and does not call for confidentiality
   protection.  Since time zone information is used in many critical
   applications, integrity protection may be required and must be
   provided externally.

   As discussed in Section 8 of [RFC7808], transmission of time zone
   data over an insecure communication channel could result in tampered
   data, harming calendaring and scheduling operations.  As such, TZif
   data transmitted over a public communications channel MUST be
   protected with a security layer such as that provided by Transport
   Layer Security (TLS) [RFC8446].

8.  Privacy Considerations

   The Time Zone Information Format contains publicly available data,
   and it does not define any extensible areas that could be used to
   store private data.

   As discussed in Section 9 of [RFC7808], transmission of time zone
   data over an insecure communications channel could leak the past,
   current, or future location of a device or user.  As such, TZif data
   transmitted over a public communications channel MUST be protected
   with a confidentiality layer such as that provided by Transport Layer
   Security (TLS) [RFC8446].

9.  IANA Considerations

   IANA has updated the "Media Types" registry
   (https://www.iana.org/assignments/media-types) as follows.

   This document defines two media types [RFC6838] for the exchange of
   data utilizing the Time Zone Information Format.

9.1.  application/tzif

   Type name:  application

   Subtype name:  tzif

   Required parameters:  N/A

   Optional parameters:  N/A

   Encoding considerations:  binary

   Security considerations:  See Section 7 of RFC 9636.

   Interoperability considerations:  See Section 4 of RFC 9636.

   Published specification:  RFC 9636.

   Applications that use this media type:  This media type is designed
      for widespread use by applications that need to use or exchange
      time zone information relative to UNIX time, such as the Time Zone
      Information Compiler (zic) [ZIC] and the GNU C Library [GNU-C].
      The Time Zone Distribution Service [RFC7808] can directly use this
      media type.

   Fragment identifier considerations:  N/A

   Additional information:

      Magic number(s):  The first 4 octets are 0x54, 0x5A, 0x69, 0x66
      File extensions(s):  N/A
      Macintosh file type code(s):  N/A

   Person & email address to contact for further information:  Time Zone
      Database mailing list <tz@iana.org>

   Intended usage:  COMMON

   Restrictions on usage:  N/A

   Author:  See the "Authors' Addresses" section of RFC 9636.

   Change controller:  IETF

9.2.  application/tzif-leap

   Type name:  application

   Subtype name:  tzif-leap

   Required parameters:  none

   Optional parameters:  none

   Encoding considerations:  binary

   Security considerations:  See Section 7 of RFC 9636.

   Interoperability considerations:  See Section 4 of RFC 9636.

   Published specification:  RFC 9636.

   Applications that use this media type:  This media type is designed
      for widespread use by applications that need to use or exchange
      time zone information relative to UNIX leap time, such as the Time
      Zone Information Compiler (zic) [ZIC] and the GNU C Library
      [GNU-C].  The Time Zone Distribution Service [RFC7808] can
      directly use this media type.

   Fragment identifier considerations:  N/A

   Additional information:

      Magic number(s):  The first 4 octets are 0x54, 0x5A, 0x69, 0x66
      File extensions(s):  N/A
      Macintosh file type code(s):  N/A

   Person & email address to contact for further information:  Time Zone
      Database mailing list <tz@iana.org>

   Intended usage:  COMMON

   Restrictions on usage:  N/A

   Author:  See the "Authors' Addresses" section of RFC 9636.

   Change controller:  IETF

10.  References

10.1.  Normative References

   [GNU-C]    Free Software Foundation, "The GNU C Library",
              <https://www.gnu.org/software/libc/>.

   [ITU-R-TF.460]
              International Telecommunication Union, "Standard-frequency
              and time-signal emissions", ITU-R Recommendation TF.460,
              February 2002, <https://www.itu.int/rec/R-REC-TF.460/en>.

   [POSIX]    IEEE, "IEEE Standard for Information Technology--Portable
              Operating System Interface (POSIX(TM)) Base
              Specifications, Issue 7", POSIX.1-2017, IEEE
              Std 1003.1-2017, DOI 10.1109/IEEESTD.2018.8277153, January
              2018, <https://pubs.opengroup.org/onlinepubs/9699919799/>.

   [RFC20]    Cerf, V., "ASCII format for network interchange", STD 80,
              RFC 20, DOI 10.17487/RFC0020, October 1969,
              <https://www.rfc-editor.org/info/rfc20>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/info/rfc6838>.

   [RFC7808]  Douglass, M. and C. Daboo, "Time Zone Data Distribution
              Service", RFC 7808, DOI 10.17487/RFC7808, March 2016,
              <https://www.rfc-editor.org/info/rfc7808>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC9110]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/info/rfc9110>.

   [ZIC]      Kerrisk, M., "zic(8) - Linux manual page",
              <http://man7.org/linux/man-pages/man8/zic.8.html>.

10.2.  Informative References

   [CGPM-2022-R4]
              General Conference on Weights and Measures, "Resolution 4
              of the 27th CGPM (2022)", DOI 10.59161/CGPM2022RES4E,
              November 2022,
              <https://www.bipm.org/en/cgpm-2022/resolution-4>.

   [CLDR]     Unicode, Inc., "Unicode CLDR Project",
              <https://cldr.unicode.org/>.

   [EGGERT-TZ]
              "History for tz", commit b5318b5, June 2024,
              <https://github.com/eggert/tz/commits/main/tzfile.5>.

   [Err6426]  RFC Errata, "Erratum ID 6426", RFC 8536,
              <https://www.rfc-editor.org/errata/eid6426>.

   [Err6435]  RFC Errata, "Erratum ID 6435", RFC 8536,
              <https://www.rfc-editor.org/errata/eid6435>.

   [Err6757]  RFC Errata, "Erratum ID 6757", RFC 8536,
              <https://www.rfc-editor.org/errata/eid6757>.

   [Err7681]  RFC Errata, "Erratum ID 7681", RFC 8536,
              <https://www.rfc-editor.org/errata/eid7681>.

   [RFC5545]  Desruisseaux, B., Ed., "Internet Calendaring and
              Scheduling Core Object Specification (iCalendar)",
              RFC 5545, DOI 10.17487/RFC5545, September 2009,
              <https://www.rfc-editor.org/info/rfc5545>.

   [RFC6557]  Lear, E. and P. Eggert, "Procedures for Maintaining the
              Time Zone Database", BCP 175, RFC 6557,
              DOI 10.17487/RFC6557, February 2012,
              <https://www.rfc-editor.org/info/rfc6557>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8536]  Olson, A., Eggert, P., and K. Murchison, "The Time Zone
              Information Format (TZif)", RFC 8536,
              DOI 10.17487/RFC8536, February 2019,
              <https://www.rfc-editor.org/info/rfc8536>.

   [tz-link]  Eggert, P. and A. Olson, "Time zone and daylight saving
              time data",
              <https://www.iana.org/time-zones/repository/tz-link.html>.

Appendix A.  Common Interoperability Issues

   This section documents common problems in implementing this
   specification.  Most of these are problems in generating TZif files
   for use by readers conforming to predecessors of this specification
   [EGGERT-TZ].  The goals of this section are to help:

   1.  TZif writers output files that avoid common pitfalls in older or
       buggy TZif readers,

   2.  TZif readers avoid common pitfalls when reading files generated
       by future TZif writers, and

   3.  any future specification authors see what sort of problems arise
       when the TZif format is changed.

   When new versions of the TZif format have been defined, a design goal
   has been that a reader can successfully use a TZif file even if the
   file is of a later TZif version than what the reader was designed
   for.  When complete compatibility was not achieved, an attempt was
   made to limit glitches to rarely used timestamps and allow simple
   partial workarounds in writers designed to generate newer-version
   data useful even for older-version readers.  This section attempts to
   document these compatibility issues and workarounds as well as other
   common bugs in readers.

   Interoperability problems with TZif include the following:

   *  Some readers examine only version 1 data.  As a partial
      workaround, a writer can output as much version 1 data as
      possible.  However, a reader should ignore version 1 data and use
      version 2+ data, even if the reader's timestamps have only 32
      bits.

   *  Some readers designed for version 2 might mishandle timestamps
      after a version 3 or higher file's last transition, because they
      cannot parse extensions to POSIX in the TZ-like string.  As a
      partial workaround, a writer can output more transitions than
      necessary, so that only far-future timestamps are mishandled by
      version 2 readers.

   *  Some readers designed for version 2 do not support permanent
      daylight saving time with transitions after 24:00 -- e.g., a TZ
      string "EST5EDT,0/0,J365/25" denoting permanent Eastern Daylight
      Time (-04).  As a workaround, a writer can substitute standard
      time for two time zones east, e.g., "XXX3EDT4,0/0,J365/23" for a
      time zone with a never-used standard time (XXX, -03) and negative
      daylight saving time (EDT, -04) all year.  Alternatively, as a
      partial workaround, a writer can substitute standard time for the
      next time zone east -- e.g., "AST4" for permanent Atlantic
      Standard Time (-04).

   *  Some readers designed for version 2 or 3 and that require strict
      conformance to [RFC8536] reject version 4 files whose leap-second
      tables are truncated at the start or end in expiration times.

   *  Some readers ignore the footer and instead predict future
      timestamps from the time type of the last transition.  As a
      partial workaround, a writer can output more transitions than
      necessary.

   *  Some readers do not use time type 0 for timestamps before the
      first transition, in that they infer a time type using a heuristic
      that does not always select time type 0.  As a partial workaround,
      a writer can output a placeholder (no-op) first transition at an
      early time.

   *  Some readers mishandle timestamps before the first transition that
      has a timestamp that is not less than -2^31.  Readers that support
      only 32-bit timestamps are likely to be more prone to this
      problem, for example, when they process 64-bit transitions, only
      some of which are representable in 32 bits.  As a partial
      workaround, a writer can output a placeholder transition at
      timestamp -2^31.

   *  Some readers mishandle a transition if its timestamp has the
      minimum possible signed 64-bit value.  Timestamps less than -2^59
      are not recommended.

   *  Some readers mishandle POSIX-style TZ strings that contain "<" or
      ">".  As a partial workaround, a writer can avoid using "<" or ">"
      for time zone abbreviations containing only alphabetic characters.

   *  Many readers mishandle time zone abbreviations that contain non-
      ASCII characters.  These characters are not recommended.

   *  Some readers may mishandle time zone abbreviations that contain
      fewer than 3 or more than 6 characters or that contain ASCII
      characters other than alphanumerics, "-", and "+".  These
      abbreviations are not recommended.

   *  This specification does not dictate how readers should deal with
      timestamps when local time is unspecified.  Common practice is for
      readers to report UT with designation string "-00".  A reader
      could return an error indication instead.

   *  Some readers mishandle TZif files that specify daylight saving
      time UT offsets that are less than the UT offsets for the
      corresponding standard time.  These readers do not support
      locations like Ireland, which uses the equivalent of the POSIX TZ
      string "IST-1GMT0,M10.5.0,M3.5.0/1", observing standard time (IST,
      +01) in summer and daylight saving time (GMT, +00) in winter.  As
      a partial workaround, a writer can output data for the equivalent
      of the POSIX TZ string "GMT0IST,M3.5.0/1,M10.5.0", thus swapping
      standard and daylight saving time.  Although this workaround
      misidentifies which part of the year uses daylight saving time, it
      records UT offsets and time zone abbreviations correctly.

   *  Some readers generate ambiguous timestamps for positive leap
      seconds that occur when the UTC offset is not a multiple of 60
      seconds.  For example, with UTC offset +01:23:45 and a positive
      leap second 78796801 (1972-06-30 23:59:60 UTC), some readers will
      map both 78796800 and 78796801 to 01:23:45 local time the next day
      instead of mapping the latter to 01:23:46, and they will map
      78796815 to 01:23:59 instead of to 01:23:60.  This has not yet
      been a practical problem, since no civil authority has observed
      such UTC offsets since leap seconds were introduced in 1972.

   Some interoperability problems are reader bugs that are listed here
   mostly as warnings to developers of readers.

   *  Some readers do not support negative timestamps.  Developers of
      distributed applications should keep this in mind if they need to
      deal with pre-1970 data.

   *  Some readers mishandle timestamps before the first transition that
      has a non-negative timestamp.  Readers that do not support
      negative timestamps are likely to be more prone to this problem.

   *  Some readers mishandle time zone abbreviations like "-08" that
      contain "+", "-", or digits.

   *  Some readers mishandle UT offsets that are out of the conventional
      range of -12 through +12 hours and so do not support locations
      like Kiritimati that are outside this range.

   *  Some readers mishandle UT offsets in the range [-3599, -1] seconds
      from UT because they integer-divide the offset by 3600 to get 0
      and then display the hour part as "+00".

   *  Some readers mishandle UT offsets that are not a multiple of one
      hour, 15 minutes, or 1 minute.

Appendix B.  Example TZif Files

   The following sections contain annotated hexadecimal dumps of example
   TZif files.

   These examples should only be considered informative.  Although the
   example data entries are current as of the publication date of this
   document, the data will likely change in the future as leap seconds
   are added and changes are made to civil time.

B.1.  Version 1 File Representing UTC (with Leap Seconds)

   +========+=============+==================+========================+
   | File   | Hexadecimal | Record Name /    | Field Value            |
   | Offset | Octets      | Field Name       |                        |
   +========+=============+==================+========================+
   | 000    | 54 5a 69 66 | magic            | "TZif"                 |
   +--------+-------------+------------------+------------------------+
   | 004    | 00          | version          | 0 (1)                  |
   +--------+-------------+------------------+------------------------+
   | 005    | 00 00 00 00 |                                           |
   |        | 00 00 00 00 |                                           |
   |        | 00 00 00 00 |                                           |
   |        | 00 00 00    |                                           |
   +--------+-------------+------------------+------------------------+
   | 020    | 00 00 00 01 | isutcnt          | 1                      |
   +--------+-------------+------------------+------------------------+
   | 024    | 00 00 00 01 | isstdcnt         | 1                      |
   +--------+-------------+------------------+------------------------+
   | 028    | 00 00 00 1b | leapcnt          | 27                     |
   +--------+-------------+------------------+------------------------+
   | 032    | 00 00 00 00 | timecnt          | 0                      |
   +--------+-------------+------------------+------------------------+
   | 036    | 00 00 00 01 | typecnt          | 1                      |
   +--------+-------------+------------------+------------------------+
   | 040    | 00 00 00 04 | charcnt          | 4                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[0] |                        |
   +--------+-------------+------------------+------------------------+
   | 044    | 00 00 00 00 | utoff            | 0 (+00:00)             |
   +--------+-------------+------------------+------------------------+
   | 048    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 049    | 00          | desigidx         | 0                      |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 050    | 55 54 43 00 | designations[0]  | "UTC\0"                |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[0]    |                        |
   +--------+-------------+------------------+------------------------+
   | 054    | 04 b2 58 00 | occurrence       | 78796800               |
   |        |             |                  | (1972-06-30T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 058    | 00 00 00 01 | correction       | 1                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[1]    |                        |
   +--------+-------------+------------------+------------------------+
   | 062    | 05 a4 ec 01 | occurrence       | 94694401               |
   |        |             |                  | (1972-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 066    | 00 00 00 02 | correction       | 2                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[2]    |                        |
   +--------+-------------+------------------+------------------------+
   | 070    | 07 86 1f 82 | occurrence       | 126230402              |
   |        |             |                  | (1973-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 074    | 00 00 00 03 | correction       | 3                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[3]    |                        |
   +--------+-------------+------------------+------------------------+
   | 078    | 09 67 53 03 | occurrence       | 157766403              |
   |        |             |                  | (1974-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 082    | 00 00 00 04 | correction       | 4                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[4]    |                        |
   +--------+-------------+------------------+------------------------+
   | 086    | 0b 48 86 84 | occurrence       | 189302404              |
   |        |             |                  | (1975-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 090    | 00 00 00 05 | correction       | 5                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[5]    |                        |
   +--------+-------------+------------------+------------------------+
   | 094    | 0d 2b 0b 85 | occurrence       | 220924805              |
   |        |             |                  | (1976-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 098    | 00 00 00 06 | correction       | 6                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[6]    |                        |
   +--------+-------------+------------------+------------------------+
   | 102    | 0f 0c 3f 06 | occurrence       | 252460806              |
   |        |             |                  | (1977-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 106    | 00 00 00 07 | correction       | 7                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[7]    |                        |
   +--------+-------------+------------------+------------------------+
   | 110    | 10 ed 72 87 | occurrence       | 283996807              |
   |        |             |                  | (1978-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 114    | 00 00 00 08 | correction       | 8                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[8]    |                        |
   +--------+-------------+------------------+------------------------+
   | 118    | 12 ce a6 08 | occurrence       | 315532808              |
   |        |             |                  | (1979-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 122    | 00 00 00 09 | correction       | 9                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[9]    |                        |
   +--------+-------------+------------------+------------------------+
   | 126    | 15 9f ca 89 | occurrence       | 362793609              |
   |        |             |                  | (1981-06-30T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 130    | 00 00 00 0a | correction       | 10                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[10]   |                        |
   +--------+-------------+------------------+------------------------+
   | 134    | 17 80 fe 0a | occurrence       | 394329610              |
   |        |             |                  | (1982-06-30T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 138    | 00 00 00 0b | correction       | 11                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[11]   |                        |
   +--------+-------------+------------------+------------------------+
   | 142    | 19 62 31 8b | occurrence       | 425865611              |
   |        |             |                  | (1983-06-30T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 146    | 00 00 00 0c | correction       | 12                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[12]   |                        |
   +--------+-------------+------------------+------------------------+
   | 150    | 1d 25 ea 0c | occurrence       | 489024012              |
   |        |             |                  | (1985-06-30T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 154    | 00 00 00 0d | correction       | 13                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[13]   |                        |
   +--------+-------------+------------------+------------------------+
   | 158    | 21 da e5 0d | occurrence       | 567993613              |
   |        |             |                  | (1987-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 162    | 00 00 00 0e | correction       | 14                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[14]   |                        |
   +--------+-------------+------------------+------------------------+
   | 166    | 25 9e 9d 8e | occurrence       | 631152014              |
   |        |             |                  | (1989-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 170    | 00 00 00 0f | correction       | 15                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[15]   |                        |
   +--------+-------------+------------------+------------------------+
   | 174    | 27 7f d1 0f | occurrence       | 662688015              |
   |        |             |                  | (1990-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 178    | 00 00 00 10 | correction       | 16                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[16]   |                        |
   +--------+-------------+------------------+------------------------+
   | 182    | 2a 50 f5 90 | occurrence       | 709948816              |
   |        |             |                  | (1992-06-30T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 186    | 00 00 00 11 | correction       | 17                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[17]   |                        |
   +--------+-------------+------------------+------------------------+
   | 190    | 2c 32 29 11 | occurrence       | 741484817              |
   |        |             |                  | (1993-06-30T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 194    | 00 00 00 12 | correction       | 18                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[18]   |                        |
   +--------+-------------+------------------+------------------------+
   | 198    | 2e 13 5c 92 | occurrence       | 773020818              |
   |        |             |                  | (1994-06-30T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 202    | 00 00 00 13 | correction       | 19                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[19]   |                        |
   +--------+-------------+------------------+------------------------+
   | 206    | 30 e7 24 13 | occurrence       | 820454419              |
   |        |             |                  | (1995-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 210    | 00 00 00 14 | correction       | 20                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[20]   |                        |
   +--------+-------------+------------------+------------------------+
   | 214    | 33 b8 48 94 | occurrence       | 867715220              |
   |        |             |                  | (1997-06-30T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 218    | 00 00 00 15 | correction       | 21                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[21]   |                        |
   +--------+-------------+------------------+------------------------+
   | 222    | 36 8c 10 15 | occurrence       | 915148821              |
   |        |             |                  | (1998-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 226    | 00 00 00 16 | correction       | 22                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[22]   |                        |
   +--------+-------------+------------------+------------------------+
   | 230    | 43 b7 1b 96 | occurrence       | 1136073622             |
   |        |             |                  | (2005-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 234    | 00 00 00 17 | correction       | 23                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[23]   |                        |
   +--------+-------------+------------------+------------------------+
   | 238    | 49 5c 07 97 | occurrence       | 1230768023             |
   |        |             |                  | (2008-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 242    | 00 00 00 18 | correction       | 24                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[24]   |                        |
   +--------+-------------+------------------+------------------------+
   | 246    | 4f ef 93 18 | occurrence       | 1341100824             |
   |        |             |                  | (2012-06-30T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 250    | 00 00 00 19 | correction       | 25                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[25]   |                        |
   +--------+-------------+------------------+------------------------+
   | 254    | 55 93 2d 99 | occurrence       | 1435708825             |
   |        |             |                  | (2015-06-30T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 258    | 00 00 00 1a | correction       | 26                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | leapsecond[26]   |                        |
   +--------+-------------+------------------+------------------------+
   | 262    | 58 68 46 9a | occurrence       | 1483228826             |
   |        |             |                  | (2016-12-31T23:59:60Z) |
   +--------+-------------+------------------+------------------------+
   | 266    | 00 00 00 1b | correction       | 27                     |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 270    | 00          | standard/wall[0] | 0 (wall)               |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 271    | 00          | UT/local[0]      | 0 (local)              |
   +--------+-------------+------------------+------------------------+

                                 Table 1

   To determine TAI corresponding to 2000-01-01T00:00:00Z
   (UNIX time = 946684800), the following procedure would be followed:

   1.  Find the latest leap-second occurrence prior to the time of
       interest (leapsecond[21]) and note the correction value
       (LEAPCORR = 22).

   2.  Add LEAPCORR + 10 to the time of interest to yield TAI of
       2000-01-01T00:00:32.

B.2.  Version 2 File Representing Pacific/Honolulu

   +========+=============+==================+========================+
   | File   | Hexadecimal | Record Name /    | Field Value            |
   | Offset | Octets      | Field Name       |                        |
   +========+=============+==================+========================+
   | 000    | 54 5a 69 66 | magic            | "TZif"                 |
   +--------+-------------+------------------+------------------------+
   | 004    | 32          | version          | '2' (2)                |
   +--------+-------------+------------------+------------------------+
   | 005    | 00 00 00 00 |                                           |
   |        | 00 00 00 00 |                                           |
   |        | 00 00 00 00 |                                           |
   |        | 00 00 00    |                                           |
   +--------+-------------+------------------+------------------------+
   | 020    | 00 00 00 06 | isutcnt          | 6                      |
   +--------+-------------+------------------+------------------------+
   | 024    | 00 00 00 06 | isstdcnt         | 6                      |
   +--------+-------------+------------------+------------------------+
   | 028    | 00 00 00 00 | leapcnt          | 0                      |
   +--------+-------------+------------------+------------------------+
   | 032    | 00 00 00 07 | timecnt          | 7                      |
   +--------+-------------+------------------+------------------------+
   | 036    | 00 00 00 06 | typecnt          | 6                      |
   +--------+-------------+------------------+------------------------+
   | 040    | 00 00 00 14 | charcnt          | 20                     |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 044    | 80 00 00 00 | trans time[0]    | -2147483648            |
   |        |             |                  | (1901-12-13T20:45:52Z) |
   +--------+-------------+------------------+------------------------+
   | 048    | bb 05 43 48 | trans time[1]    | -1157283000            |
   |        |             |                  | (1933-04-30T12:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 052    | bb 21 71 58 | trans time[2]    | -1155436200            |
   |        |             |                  | (1933-05-21T21:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 056    | cb 89 3d c8 | trans time[3]    | -880198200             |
   |        |             |                  | (1942-02-09T12:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 060    | d2 23 f4 70 | trans time[4]    | -769395600             |
   |        |             |                  | (1945-08-14T23:00:00Z) |
   +--------+-------------+------------------+------------------------+
   | 064    | d2 61 49 38 | trans time[5]    | -765376200             |
   |        |             |                  | (1945-09-30T11:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 068    | d5 8d 73 48 | trans time[6]    | -712150200             |
   |        |             |                  | (1947-06-08T12:30:00Z) |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 072    | 01          | trans type[0]    | 1                      |
   +--------+-------------+------------------+------------------------+
   | 073    | 02          | trans type[1]    | 2                      |
   +--------+-------------+------------------+------------------------+
   | 074    | 01          | trans type[2]    | 1                      |
   +--------+-------------+------------------+------------------------+
   | 075    | 03          | trans type[3]    | 3                      |
   +--------+-------------+------------------+------------------------+
   | 076    | 04          | trans type[4]    | 4                      |
   +--------+-------------+------------------+------------------------+
   | 077    | 01          | trans type[5]    | 1                      |
   +--------+-------------+------------------+------------------------+
   | 078    | 05          | trans type[6]    | 5                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[0] |                        |
   +--------+-------------+------------------+------------------------+
   | 079    | ff ff 6c 02 | utoff            | -37886 (-10:31:26)     |
   +--------+-------------+------------------+------------------------+
   | 083    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 084    | 00          | desigidx         | 0                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[1] |                        |
   +--------+-------------+------------------+------------------------+
   | 085    | ff ff 6c 58 | utoff            | -37800 (-10:30)        |
   +--------+-------------+------------------+------------------------+
   | 089    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 090    | 04          | desigidx         | 4                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[2] |                        |
   +--------+-------------+------------------+------------------------+
   | 091    | ff ff 7a 68 | utoff            | -34200 (-09:30)        |
   +--------+-------------+------------------+------------------------+
   | 095    | 01          | isdst            | 1 (yes)                |
   +--------+-------------+------------------+------------------------+
   | 096    | 08          | desigidx         | 8                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[3] |                        |
   +--------+-------------+------------------+------------------------+
   | 097    | ff ff 7a 68 | utoff            | -34200 (-09:30)        |
   +--------+-------------+------------------+------------------------+
   | 101    | 01          | isdst            | 1 (yes)                |
   +--------+-------------+------------------+------------------------+
   | 102    | 0c          | desigidx         | 12                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[4] |                        |
   +--------+-------------+------------------+------------------------+
   | 103    | ff ff 7a 68 | utoff            | -34200 (-09:30)        |
   +--------+-------------+------------------+------------------------+
   | 107    | 01          | isdst            | 1 (yes)                |
   +--------+-------------+------------------+------------------------+
   | 108    | 10          | desigidx         | 16                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[5] |                        |
   +--------+-------------+------------------+------------------------+
   | 109    | ff ff 73 60 | utoff            | -36000 (-10:00)        |
   +--------+-------------+------------------+------------------------+
   | 113    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 114    | 04          | desigidx         | 4                      |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 115    | 4c 4d 54 00 | designations[0]  | "LMT\0"                |
   +--------+-------------+------------------+------------------------+
   | 119    | 48 53 54 00 | designations[4]  | "HST\0"                |
   +--------+-------------+------------------+------------------------+
   | 123    | 48 44 54 00 | designations[8]  | "HDT\0"                |
   +--------+-------------+------------------+------------------------+
   | 127    | 48 57 54 00 | designations[12] | "HWT\0"                |
   +--------+-------------+------------------+------------------------+
   | 131    | 48 50 54 00 | designations[16] | "HPT\0"                |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 135    | 00          | standard/wall[0] | 0 (wall)               |
   +--------+-------------+------------------+------------------------+
   | 136    | 00          | standard/wall[1] | 0 (wall)               |
   +--------+-------------+------------------+------------------------+
   | 137    | 00          | standard/wall[2] | 0 (wall)               |
   +--------+-------------+------------------+------------------------+
   | 138    | 00          | standard/wall[3] | 0 (wall)               |
   +--------+-------------+------------------+------------------------+
   | 139    | 01          | standard/wall[4] | 1 (standard)           |
   +--------+-------------+------------------+------------------------+
   | 140    | 00          | standard/wall[5] | 0 (wall)               |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 141    | 00          | UT/local[0]      | 0 (local)              |
   +--------+-------------+------------------+------------------------+
   | 142    | 00          | UT/local[1]      | 0 (local)              |
   +--------+-------------+------------------+------------------------+
   | 143    | 00          | UT/local[2]      | 0 (local)              |
   +--------+-------------+------------------+------------------------+
   | 144    | 00          | UT/local[3]      | 0 (local)              |
   +--------+-------------+------------------+------------------------+
   | 145    | 01          | UT/local[4]      | 1 (UT)                 |
   +--------+-------------+------------------+------------------------+
   | 146    | 00          | UT/local[5]      | 0 (local)              |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 147    | 54 5a 69 66 | magic            | "TZif"                 |
   +--------+-------------+------------------+------------------------+
   | 151    | 32          | version          | '2' (2)                |
   +--------+-------------+------------------+------------------------+
   | 152    | 00 00 00 00 |                                           |
   |        | 00 00 00 00 |                                           |
   |        | 00 00 00 00 |                                           |
   |        | 00 00 00    |                                           |
   +--------+-------------+------------------+------------------------+
   | 167    | 00 00 00 06 | isutcnt          | 6                      |
   +--------+-------------+------------------+------------------------+
   | 171    | 00 00 00 06 | isstdcnt         | 6                      |
   +--------+-------------+------------------+------------------------+
   | 175    | 00 00 00 00 | leapcnt          | 0                      |
   +--------+-------------+------------------+------------------------+
   | 179    | 00 00 00 07 | timecnt          | 7                      |
   +--------+-------------+------------------+------------------------+
   | 183    | 00 00 00 06 | typecnt          | 6                      |
   +--------+-------------+------------------+------------------------+
   | 187    | 00 00 00 14 | charcnt          | 20                     |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 191    | ff ff ff ff | trans time[0]    | -2334101314            |
   |        | 74 e0 70 be |                  | (1896-01-13T22:31:26Z) |
   +--------+-------------+------------------+------------------------+
   | 199    | ff ff ff ff | trans time[1]    | -1157283000            |
   |        | bb 05 43 48 |                  | (1933-04-30T12:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 207    | ff ff ff ff | trans time[2]    | -1155436200            |
   |        | bb 21 71 58 |                  | (1933-05-21T21:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 215    | ff ff ff ff | trans time[3]    | -880198200             |
   |        | cb 89 3d c8 |                  | (1942-02-09T12:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 223    | ff ff ff ff | trans time[4]    | -769395600             |
   |        | d2 23 f4 70 |                  | (1945-08-14T23:00:00Z) |
   +--------+-------------+------------------+------------------------+
   | 231    | ff ff ff ff | trans time[5]    | -765376200             |
   |        | d2 61 49 38 |                  | (1945-09-30T11:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 239    | ff ff ff ff | trans time[6]    | -712150200             |
   |        | d5 8d 73 48 |                  | (1947-06-08T12:30:00Z) |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 247    | 01          | trans type[0]    | 1                      |
   +--------+-------------+------------------+------------------------+
   | 248    | 02          | trans type[1]    | 2                      |
   +--------+-------------+------------------+------------------------+
   | 249    | 01          | trans type[2]    | 1                      |
   +--------+-------------+------------------+------------------------+
   | 250    | 03          | trans type[3]    | 3                      |
   +--------+-------------+------------------+------------------------+
   | 251    | 04          | trans type[4]    | 4                      |
   +--------+-------------+------------------+------------------------+
   | 252    | 01          | trans type[5]    | 1                      |
   +--------+-------------+------------------+------------------------+
   | 253    | 05          | trans type[6]    | 5                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[0] |                        |
   +--------+-------------+------------------+------------------------+
   | 254    | ff ff 6c 02 | utoff            | -37886 (-10:31:26)     |
   +--------+-------------+------------------+------------------------+
   | 258    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 259    | 00          | desigidx         | 0                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[1] |                        |
   +--------+-------------+------------------+------------------------+
   | 260    | ff ff 6c 58 | utoff            | -37800 (-10:30)        |
   +--------+-------------+------------------+------------------------+
   | 264    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 265    | 04          | desigidx         | 4                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[2] |                        |
   +--------+-------------+------------------+------------------------+
   | 266    | ff ff 7a 68 | utoff            | -34200 (-09:30)        |
   +--------+-------------+------------------+------------------------+
   | 270    | 01          | isdst            | 1 (yes)                |
   +--------+-------------+------------------+------------------------+
   | 271    | 08          | desigidx         | 8                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[3] |                        |
   +--------+-------------+------------------+------------------------+
   | 272    | ff ff 7a 68 | utoff            | -34200 (-09:30)        |
   +--------+-------------+------------------+------------------------+
   | 276    | 01          | isdst            | 1 (yes)                |
   +--------+-------------+------------------+------------------------+
   | 277    | 0c          | desigidx         | 12                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[4] |                        |
   +--------+-------------+------------------+------------------------+
   | 278    | ff ff 7a 68 | utoff            | -34200 (-09:30)        |
   +--------+-------------+------------------+------------------------+
   | 282    | 01          | isdst            | 1 (yes)                |
   +--------+-------------+------------------+------------------------+
   | 283    | 10          | desigidx         | 16                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[5] |                        |
   +--------+-------------+------------------+------------------------+
   | 284    | ff ff 73 60 | utoff            | -36000 (-10:00)        |
   +--------+-------------+------------------+------------------------+
   | 288    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 289    | 04          | desigidx         | 4                      |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 290    | 4c 4d 54 00 | designations[0]  | "LMT\0"                |
   +--------+-------------+------------------+------------------------+
   | 294    | 48 53 54 00 | designations[4]  | "HST\0"                |
   +--------+-------------+------------------+------------------------+
   | 298    | 48 44 54 00 | designations[8]  | "HDT\0"                |
   +--------+-------------+------------------+------------------------+
   | 302    | 48 57 54 00 | designations[12] | "HWT\0"                |
   +--------+-------------+------------------+------------------------+
   | 306    | 48 50 54 00 | designations[16] | "HPT\0"                |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 310    | 00          | standard/wall[0] | 0 (wall)               |
   +--------+-------------+------------------+------------------------+
   | 311    | 00          | standard/wall[1] | 0 (wall)               |
   +--------+-------------+------------------+------------------------+
   | 312    | 00          | standard/wall[2] | 0 (wall)               |
   +--------+-------------+------------------+------------------------+
   | 313    | 00          | standard/wall[3] | 0 (wall)               |
   +--------+-------------+------------------+------------------------+
   | 314    | 01          | standard/wall[4] | 1 (standard)           |
   +--------+-------------+------------------+------------------------+
   | 315    | 00          | standard/wall[5] | 0 (wall)               |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 316    | 00          | UT/local[0]      | 0 (local)              |
   +--------+-------------+------------------+------------------------+
   | 317    | 00          | UT/local[1]      | 0 (local)              |
   +--------+-------------+------------------+------------------------+
   | 318    | 00          | UT/local[2]      | 0 (local)              |
   +--------+-------------+------------------+------------------------+
   | 319    | 00          | UT/local[3]      | 0 (local)              |
   +--------+-------------+------------------+------------------------+
   | 320    | 01          | UT/local[4]      | 1 (UT)                 |
   +--------+-------------+------------------+------------------------+
   | 321    | 00          | UT/local[5]      | 0 (local)              |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 322    | 0a          | NL               | '\n'                   |
   +--------+-------------+------------------+------------------------+
   | 323    | 48 53 54 31 | TZ string        | "HST10"                |
   |        | 30          |                  |                        |
   +--------+-------------+------------------+------------------------+
   | 328    | 0a          | NL               | '\n'                   |
   +--------+-------------+------------------+------------------------+

                                 Table 2

   To determine the local time in this time zone corresponding to
   1933-05-04T12:00:00Z (UNIX time = -1156939200), the following
   procedure would be followed:

   1.  Find the latest time transition prior to the time of interest
       (trans time[1]).

   2.  Reference the corresponding transition type (trans type[1]) to
       determine the local time type index (2).

   3.  Reference the corresponding local time type (localtimetype[2]) to
       determine the offset from UTC (-09:30), the daylight saving
       indicator (1 = yes), and the index into the time zone designation
       strings (8).

   4.  Look up the corresponding time zone designation string
       (designations[8] = "HDT").

   5.  Add the UTC offset to the time of interest to yield a local
       daylight saving time of 1933-05-04T02:30:00-09:30 (HDT).

   To determine the local time in this time zone corresponding to
   2019-01-01T00:00:00Z (UNIX time = 1546300800), the following
   procedure would be followed:

   1.  Find the latest time transition prior to the time of interest
       (there is no such transition).

   2.  Look up the TZ string in the footer ("HST10"), which indicates
       that the time zone designation is "HST" year-round and the offset
       to UTC is 10:00.

   3.  Subtract the UTC offset from the time of interest to yield a
       standard local time of 2018-12-31T14:00:00-10:00 (HST).

B.3.  Truncated Version 2 File Representing Pacific/Johnston

   The following TZif file has been truncated to end on
   2004-06-161T00:00:00Z (the atoll was abandoned sometime on
   2004-06-15).

   In this example:

   *  The version 1 header contains only the required minimum data,
      which will be ignored by readers.

   *  The version 2 header leverages the fact that, by specifying
      'isutcnt' and 'isstdcnt' as zero, all transition times associated
      with local time types are assumed to be specified as local wall-
      clock time (see the definitions of UT/local indicators and
      standard/wall indicators in Section 3.2).

   *  The time type of the last transition has designation "-00",
      indicating that local time is unspecified.

   *  The TZ string is empty, indicating that there are no known future
      transitions.

   +========+=============+==================+========================+
   | File   | Hexadecimal | Record Name /    | Field Value            |
   | Offset | Octets      | Field Name       |                        |
   +========+=============+==================+========================+
   | 000    | 54 5a 69 66 | magic            | "TZif"                 |
   +--------+-------------+------------------+------------------------+
   | 004    | 32          | version          | '2' (2)                |
   +--------+-------------+------------------+------------------------+
   | 005    | 00 00 00 00 |                  |                        |
   |        | 00 00 00 00 |                  |                        |
   |        | 00 00 00 00 |                  |                        |
   |        | 00 00 00    |                  |                        |
   +--------+-------------+------------------+------------------------+
   | 020    | 00 00 00 00 | isutcnt          | 0                      |
   +--------+-------------+------------------+------------------------+
   | 024    | 00 00 00 00 | isstdcnt         | 0                      |
   +--------+-------------+------------------+------------------------+
   | 028    | 00 00 00 00 | leapcnt          | 0                      |
   +--------+-------------+------------------+------------------------+
   | 032    | 00 00 00 00 | timecnt          | 0                      |
   +--------+-------------+------------------+------------------------+
   | 036    | 00 00 00 01 | typecnt          | 1                      |
   +--------+-------------+------------------+------------------------+
   | 040    | 00 00 00 01 | charcnt          | 1                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[0] |                        |
   +--------+-------------+------------------+------------------------+
   | 044    | 00 00 00 00 | utoff            | 0 (+00:00)             |
   +--------+-------------+------------------+------------------------+
   | 048    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 049    | 00          | desigidx         | 0                      |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 050    | 00          | designations[0]  | "\0"                   |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 051    | 54 5a 69 66 | magic            | "TZif"                 |
   +--------+-------------+------------------+------------------------+
   | 055    | 32          | version          | '2' (2)                |
   +--------+-------------+------------------+------------------------+
   | 056    | 00 00 00 00 |                                           |
   |        | 00 00 00 00 |                                           |
   |        | 00 00 00 00 |                                           |
   |        | 00 00 00    |                                           |
   +--------+-------------+------------------+------------------------+
   | 071    | 00 00 00 00 | isutcnt          | 0                      |
   +--------+-------------+------------------+------------------------+
   | 075    | 00 00 00 00 | isstdcnt         | 0                      |
   +--------+-------------+------------------+------------------------+
   | 079    | 00 00 00 00 | leapcnt          | 0                      |
   +--------+-------------+------------------+------------------------+
   | 083    | 00 00 00 08 | timecnt          | 8                      |
   +--------+-------------+------------------+------------------------+
   | 087    | 00 00 00 07 | typecnt          | 7                      |
   +--------+-------------+------------------+------------------------+
   | 091    | 00 00 00 18 | charcnt          | 24                     |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 095    | ff ff ff ff | trans time[0]    | -2334101314            |
   |        | 74 e0 70 be |                  | (1896-01-13T22:31:26Z) |
   +--------+-------------+------------------+------------------------+
   | 103    | ff ff ff ff | trans time[1]    | -1157283000            |
   |        | bb 05 43 48 |                  | (1933-04-30T12:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 111    | ff ff ff ff | trans time[2]    | -1155436200            |
   |        | bb 21 71 58 |                  | (1933-05-21T21:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 119    | ff ff ff ff | trans time[3]    | -880198200             |
   |        | cb 89 3d c8 |                  | (1942-02-09T12:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 127    | ff ff ff ff | trans time[4]    | -769395600             |
   |        | d2 23 f4 70 |                  | (1945-08-14T23:00:00Z) |
   +--------+-------------+------------------+------------------------+
   | 135    | ff ff ff ff | trans time[5]    | -765376200             |
   |        | d2 61 49 38 |                  | (1945-09-30T11:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 143    | ff ff ff ff | trans time[6]    | -712150200             |
   |        | d5 8d 73 48 |                  | (1947-06-08T12:30:00Z) |
   +--------+-------------+------------------+------------------------+
   | 151    | 00 00 00 00 | trans time[7]    | 1087344000             |
   |        | 40 cf 8d 80 |                  | (2004-06-16T00:00:00Z) |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 159    | 02          | trans type[0]    | 2                      |
   +--------+-------------+------------------+------------------------+
   | 160    | 03          | trans type[1]    | 3                      |
   +--------+-------------+------------------+------------------------+
   | 161    | 02          | trans type[2]    | 2                      |
   +--------+-------------+------------------+------------------------+
   | 162    | 04          | trans type[3]    | 4                      |
   +--------+-------------+------------------+------------------------+
   | 163    | 05          | trans type[4]    | 5                      |
   +--------+-------------+------------------+------------------------+
   | 164    | 02          | trans type[5]    | 2                      |
   +--------+-------------+------------------+------------------------+
   | 165    | 06          | trans type[6]    | 6                      |
   +--------+-------------+------------------+------------------------+
   | 166    | 01          | trans type[7]    | 1                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[0] |                        |
   +--------+-------------+------------------+------------------------+
   | 167    | ff ff 6c 02 | utoff            | -37886 (-10:31:26)     |
   +--------+-------------+------------------+------------------------+
   | 171    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 172    | 04          | desigidx         | 4                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[1] |                        |
   +--------+-------------+------------------+------------------------+
   | 173    | 00 00 00 00 | utoff            | 0 (+00:00)             |
   +--------+-------------+------------------+------------------------+
   | 177    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 178    | 00          | desigidx         | 0                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[2] |                        |
   +--------+-------------+------------------+------------------------+
   | 179    | ff ff 6c 58 | utoff            | -37800 (-10:30)        |
   +--------+-------------+------------------+------------------------+
   | 183    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 184    | 08          | desigidx         | 8                      |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[3] |                        |
   +--------+-------------+------------------+------------------------+
   | 185    | ff ff 7a 68 | utoff            | -34200 (-09:30)        |
   +--------+-------------+------------------+------------------------+
   | 189    | 01          | isdst            | 1 (yes)                |
   +--------+-------------+------------------+------------------------+
   | 190    | 0c          | desigidx         | 12                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[4] |                        |
   +--------+-------------+------------------+------------------------+
   | 191    | ff ff 7a 68 | utoff            | -34200 (-09:30)        |
   +--------+-------------+------------------+------------------------+
   | 195    | 01          | isdst            | 1 (yes)                |
   +--------+-------------+------------------+------------------------+
   | 196    | 10          | desigidx         | 16                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[5] |                        |
   +--------+-------------+------------------+------------------------+
   | 197    | ff ff 7a 68 | utoff            | -34200 (-09:30)        |
   +--------+-------------+------------------+------------------------+
   | 201    | 01          | isdst            | 1 (yes)                |
   +--------+-------------+------------------+------------------------+
   | 202    | 14          | desigidx         | 20                     |
   +--------+-------------+------------------+------------------------+
   +----------------------+------------------+------------------------+
   |                      | localtimetype[6] |                        |
   +--------+-------------+------------------+------------------------+
   | 203    | ff ff 73 60 | utoff            | -36000 (-10:00)        |
   +--------+-------------+------------------+------------------------+
   | 207    | 00          | isdst            | 0 (no)                 |
   +--------+-------------+------------------+------------------------+
   | 208    | 08          | desigidx         | 8                      |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 209    | 2d 30 30 00 | designations[0]  | "-00\0"                |
   +--------+-------------+------------------+------------------------+
   | 213    | 4c 4d 54 00 | designations[4]  | "LMT\0"                |
   +--------+-------------+------------------+------------------------+
   | 217    | 48 53 54 00 | designations[8]  | "HST\0"                |
   +--------+-------------+------------------+------------------------+
   | 221    | 48 44 54 00 | designations[12] | "HDT\0"                |
   +--------+-------------+------------------+------------------------+
   | 225    | 48 57 54 00 | designations[16] | "HWT\0"                |
   +--------+-------------+------------------+------------------------+
   | 229    | 48 50 54 00 | designations[20] | "HPT\0"                |
   +--------+-------------+------------------+------------------------+
   +--------+-------------+------------------+------------------------+
   | 233    | 0a          | NL               | '\n'                   |
   +--------+-------------+------------------+------------------------+
   | 234    |             | TZ string        | ""                     |
   +--------+-------------+------------------+------------------------+
   | 234    | 0a          | NL               | '\n'                   |
   +--------+-------------+------------------+------------------------+

                                 Table 3

B.4.  Truncated Version 3 File Representing Asia/Jerusalem

   The following TZif file has been truncated to start on
   2038-01-01T00:00:00Z.

   In this example:

   *  The start time value cannot be represented using 32 bits, so the
      version 1 header contains only the required minimum data, which
      will be ignored by readers.

   *  The version 3 header leverages the fact that, by specifying
      'isutcnt' and 'isstdcnt' as zero, all transition times associated
      with local time types are assumed to be specified as local wall-
      clock time (see the definitions of UT/local indicators and
      standard/wall indicators in Section 3.2).

   *  Time type 0 has designation "-00", indicating that local time is
      unspecified prior to the truncation time.

   *  The TZ string value has been line-wrapped for presentation
      purposes only.

   +======+===========+================+==============================+
   |File  |Hexadecimal|Record Name /   | Field Value                  |
   |Offset|Octets     |Field Name      |                              |
   +======+===========+================+==============================+
   |000   |54 5a 69 66|magic           | "TZif"                       |
   +------+-----------+----------------+------------------------------+
   |004   |33         |version         | '3' (3)                      |
   +------+-----------+----------------+------------------------------+
   |005   |00 00 00 00|                                               |
   |      |00 00 00 00|                                               |
   |      |00 00 00 00|                                               |
   |      |00 00 00   |                                               |
   +------+-----------+----------------+------------------------------+
   |020   |00 00 00 00|isutcnt         | 0                            |
   +------+-----------+----------------+------------------------------+
   |024   |00 00 00 00|isstdcnt        | 0                            |
   +------+-----------+----------------+------------------------------+
   |028   |00 00 00 00|leapcnt         | 0                            |
   +------+-----------+----------------+------------------------------+
   |032   |00 00 00 00|timecnt         | 0                            |
   +------+-----------+----------------+------------------------------+
   |036   |00 00 00 01|typecnt         | 1                            |
   +------+-----------+----------------+------------------------------+
   |040   |00 00 00 01|charcnt         | 1                            |
   +------+-----------+----------------+------------------------------+
   +------------------+----------------+------------------------------+
   |                  |localtimetype[0]|                              |
   +------+-----------+----------------+------------------------------+
   |044   |00 00 00 00|utoff           | 0 (+00:00)                   |
   +------+-----------+----------------+------------------------------+
   |048   |00         |isdst           | 0 (no)                       |
   +------+-----------+----------------+------------------------------+
   |049   |00         |desigidx        | 0                            |
   +------+-----------+----------------+------------------------------+
   +------+-----------+----------------+------------------------------+
   |050   |00         |designations[0] | "\0"                         |
   +------+-----------+----------------+------------------------------+
   +------+-----------+----------------+------------------------------+
   |051   |54 5a 69 66|magic           | "TZif"                       |
   +------+-----------+----------------+------------------------------+
   |055   |33         |version         | '3' (3)                      |
   +------+-----------+----------------+------------------------------+
   |056   |00 00 00 00|                                               |
   |      |00 00 00 00|                                               |
   |      |00 00 00 00|                                               |
   |      |00 00 00   |                                               |
   +------+-----------+----------------+------------------------------+
   |071   |00 00 00 00|isutcnt         | 0                            |
   +------+-----------+----------------+------------------------------+
   |075   |00 00 00 00|isstdcnt        | 0                            |
   +------+-----------+----------------+------------------------------+
   |079   |00 00 00 00|leapcnt         | 0                            |
   +------+-----------+----------------+------------------------------+
   |083   |00 00 00 01|timecnt         | 1                            |
   +------+-----------+----------------+------------------------------+
   |087   |00 00 00 02|typecnt         | 2                            |
   +------+-----------+----------------+------------------------------+
   |091   |00 00 00 08|charcnt         | 8                            |
   +------+-----------+----------------+------------------------------+
   +------+-----------+----------------+------------------------------+
   |095   |00 00 00 00|trans time[0]   | 2145916800                   |
   |      |7f e8 17 80|                | (2038-01-01T00:00:00Z)       |
   +------+-----------+----------------+------------------------------+
   +------+-----------+----------------+------------------------------+
   |103   |01         |trans type[0]   | 1                            |
   +------+-----------+----------------+------------------------------+
   +------------------+----------------+------------------------------+
   |                  |localtimetype[0]|                              |
   +------+-----------+----------------+------------------------------+
   |104   |00 00 00 00|utoff           | 0 (+00:00)                   |
   +------+-----------+----------------+------------------------------+
   |108   |00         |isdst           | 0 (no)                       |
   +------+-----------+----------------+------------------------------+
   |109   |00         |desigidx        | 0                            |
   +------+-----------+----------------+------------------------------+
   +------------------+----------------+------------------------------+
   |                  |localtimetype[1]|                              |
   +------+-----------+----------------+------------------------------+
   |110   |00 00 1c 20|utoff           | 7200 (+02:00)                |
   +------+-----------+----------------+------------------------------+
   |114   |00         |isdst           | 0 (no)                       |
   +------+-----------+----------------+------------------------------+
   |115   |04         |desigidx        | 4                            |
   +------+-----------+----------------+------------------------------+
   +------+-----------+----------------+------------------------------+
   |116   |2d 30 30 00|designations[0] | "-00\0"                      |
   +------+-----------+----------------+------------------------------+
   |120   |49 53 54 00|designations[4] | "IST\0"                      |
   +------+-----------+----------------+------------------------------+
   +------+-----------+----------------+------------------------------+
   |124   |0a         |NL              | '\n'                         |
   +------+-----------+----------------+------------------------------+
   |125   |49 53 54 2d|TZ string       | "IST-2IDT,M3.4.4/26,M10.5.0" |
   |      |32 49 44 54|                |                              |
   |      |2c 4d 33 2e|                |                              |
   |      |34 2e 34 2f|                |                              |
   |      |32 36 2c 4d|                |                              |
   |      |31 30 2e 35|                |                              |
   |      |2e 30      |                |                              |
   +------+-----------+----------------+------------------------------+
   |151   |0a         |NL              | '\n'                         |
   +------+-----------+----------------+------------------------------+

                                 Table 4

B.5.  Truncated Version 4 File Representing Europe/London

   The following TZif file has been truncated to start on
   2022-01-01T00:00:00Z.

   In this example:

   *  The version 1 header contains only the required minimum data,
      which will be ignored by readers.

   *  The version 4 header leverages the fact that, by specifying
      'isutcnt' and 'isstdcnt' as zero, all transition times associated
      with local time types are assumed to be specified as local wall-
      clock time (see the definitions of UT/local indicators and
      standard/wall indicators in Section 3.2).

   *  Time type 0 has designation "-00", indicating that local time is
      unspecified prior to the truncation time.

   *  The first leap-second occurrence is the most recent one prior to
      the truncation time.

   *  The last leap-second correction matches the second-to-last leap-
      second correction, indicating the expiration time of the leap-
      second table.

   *  The TZ string value has been line-wrapped for presentation
      purposes only.

   +======+===========+==================+============================+
   |File  |Hexadecimal| Record Name /    | Field Value                |
   |Offset|Octets     | Field Name       |                            |
   +======+===========+==================+============================+
   |000   |54 5a 69 66| magic            | "TZif"                     |
   +------+-----------+------------------+----------------------------+
   |004   |34         | version          | '4' (4)                    |
   +------+-----------+------------------+----------------------------+
   |005   |00 00 00 00|                                               |
   |      |00 00 00 00|                                               |
   |      |00 00 00 00|                                               |
   |      |00 00 00   |                                               |
   +------+-----------+------------------+----------------------------+
   |020   |00 00 00 00| isutcnt          | 0                          |
   +------+-----------+------------------+----------------------------+
   |024   |00 00 00 00| isstdcnt         | 0                          |
   +------+-----------+------------------+----------------------------+
   |028   |00 00 00 00| leapcnt          | 0                          |
   +------+-----------+------------------+----------------------------+
   |032   |00 00 00 00| timecnt          | 0                          |
   +------+-----------+------------------+----------------------------+
   |036   |00 00 00 01| typecnt          | 1                          |
   +------+-----------+------------------+----------------------------+
   |040   |00 00 00 01| charcnt          | 1                          |
   +------+-----------+------------------+----------------------------+
   +------------------+------------------+----------------------------+
   |                  | localtimetype[0] |                            |
   +------+-----------+------------------+----------------------------+
   |044   |00 00 00 00| utoff            | 0 (+00:00)                 |
   +------+-----------+------------------+----------------------------+
   |048   |00         | isdst            | 0 (no)                     |
   +------+-----------+------------------+----------------------------+
   |049   |00         | desigidx         | 0                          |
   +------+-----------+------------------+----------------------------+
   +------+-----------+------------------+----------------------------+
   |050   |00         | designations[0]  | "\0"                       |
   +------+-----------+------------------+----------------------------+
   +------+-----------+------------------+----------------------------+
   |051   |54 5a 69 66| magic            | "TZif"                     |
   +------+-----------+------------------+----------------------------+
   |055   |34         | version          | '4' (4)                    |
   +------+-----------+------------------+----------------------------+
   |056   |00 00 00 00|                                               |
   |      |00 00 00 00|                                               |
   |      |00 00 00 00|                                               |
   |      |00 00 00   |                                               |
   +------+-----------+------------------+----------------------------+
   |071   |00 00 00 00| isutcnt          | 0                          |
   +------+-----------+------------------+----------------------------+
   |075   |00 00 00 00| isstdcnt         | 0                          |
   +------+-----------+------------------+----------------------------+
   |079   |00 00 00 02| leapcnt          | 2                          |
   +------+-----------+------------------+----------------------------+
   |083   |00 00 00 01| timecnt          | 1                          |
   +------+-----------+------------------+----------------------------+
   |087   |00 00 00 02| typecnt          | 2                          |
   +------+-----------+------------------+----------------------------+
   |091   |00 00 00 08| charcnt          | 8                          |
   +------+-----------+------------------+----------------------------+
   +------+-----------+------------------+----------------------------+
   |095   |00 00 00 00| trans time[0]    | 1640995227                 |
   |      |61 cf 99 9b|                  | (2022-01-01T00:00:27Z)     |
   +------+-----------+------------------+----------------------------+
   +------+-----------+------------------+----------------------------+
   |103   |01         | trans type[0]    | 1                          |
   +------+-----------+------------------+----------------------------+
   +------------------+------------------+----------------------------+
   |                  | localtimetype[0] |                            |
   +------+-----------+------------------+----------------------------+
   |104   |00 00 00 00| utoff            | 0 (+00:00)                 |
   +------+-----------+------------------+----------------------------+
   |108   |00         | isdst            | 0 (no)                     |
   +------+-----------+------------------+----------------------------+
   |109   |00         | desigidx         | 0                          |
   +------+-----------+------------------+----------------------------+
   +------------------+------------------+----------------------------+
   |                  | localtimetype[1] |                            |
   +------+-----------+------------------+----------------------------+
   |110   |00 00 00 00| utoff            | 0 (+00:00)                 |
   +------+-----------+------------------+----------------------------+
   |114   |00         | isdst            | 0 (no)                     |
   +------+-----------+------------------+----------------------------+
   |115   |04         | desigidx         | 4                          |
   +------+-----------+------------------+----------------------------+
   +------+-----------+------------------+----------------------------+
   |116   |2d 30 30 00| designations[0]  | "-00\0"                    |
   +------+-----------+------------------+----------------------------+
   |120   |47 4d 54 00| designations[4]  | "GMT\0"                    |
   +------+-----------+------------------+----------------------------+
   +------------------+------------------+----------------------------+
   |                  | leapsecond[0]    |                            |
   +------+-----------+------------------+----------------------------+
   |124   |00 00 00 00| occurrence       | 1483228826                 |
   |      |58 68 46 9a|                  | (2016-12-31T23:59:60Z)     |
   +------+-----------+------------------+----------------------------+
   |132   |00 00 00 1b| correction       | 27                         |
   +------+-----------+------------------+----------------------------+
   +------------------+------------------+----------------------------+
   |                  | leapsecond[1]    |                            |
   +------+-----------+------------------+----------------------------+
   |136   |00 00 00 00| occurrence       | 1719532827                 |
   |      |66 7d fd 1b|                  | (2024-06-28T00:00:01Z)     |
   +------+-----------+------------------+----------------------------+
   |144   |00 00 00 1b| correction       | 27                         |
   +------+-----------+------------------+----------------------------+
   +------+-----------+------------------+----------------------------+
   |148   |0a         | NL               | '\n'                       |
   +------+-----------+------------------+----------------------------+
   |149   |47 4d 54 30| TZ string        | "GMT0BST,M3.5.0/1,M10.5.0" |
   |      |42 53 54 2c|                  |                            |
   |      |4d 33 2e 35|                  |                            |
   |      |2e 30 2f 31|                  |                            |
   |      |2c 4d 31 30|                  |                            |
   |      |2e 35 2e 30|                  |                            |
   +------+-----------+------------------+----------------------------+
   |173   |0a         | NL               | '\n'                       |
   +------+-----------+------------------+----------------------------+

                                 Table 5

Appendix C.  Changes from RFC 8536

   *  Added definition of Leap Second.

   *  Added specification of the version 4 format and the optional leap-
      second table truncation and expiration, along with an example and
      relevant interoperability considerations.

   *  Documented the longstanding practice that UT with designation
      string "-00" denotes unspecified local time.  Added recommendation
      that this designation string should be used for timestamps
      excluded by TZif file truncation.

   *  Required support in version 2 files for all-year daylight saving
      time, using POSIX TZ strings with negative DST, as this is not an
      extension to POSIX (Section 3.3.1).

   *  Applied erratum [Err6435].

   *  Addressed errata [Err6426], [Err6757], and [Err7681] as well as
      several other errors in the examples.

   *  Added additional interoperability considerations and common
      issues.

   *  Added an example of a TZif file truncated at the end
      (Appendix B.3).

   *  Added informational notes to Appendix B.4.

   *  Miscellaneous editorial changes.

Acknowledgments

   The authors thank the following individuals for contributing their
   ideas and support for writing this specification: Michael Douglass,
   Ned Freed, Guy Harris, Eliot Lear, Alexey Melnikov, and Tim Parenti.

Authors' Addresses

   Arthur David Olson
   Email: arthurdavidolson@gmail.com


   Paul Eggert
   University of California, Los Angeles
   Email: eggert@cs.ucla.edu


   Kenneth Murchison
   Fastmail US LLC
   Email: murch@fastmailteam.com