[tz] [PROPOSED 2/2] Update some documentation and commentary

Paul Eggert eggert at cs.ucla.edu
Mon Aug 15 23:58:04 UTC 2022

* Makefile, newctime.3, theory.html:
* tz-art.html, tz-link.html, tzfile.5:
Update some citations and remove a duplicate URL.
Prefer https: to http: where either will do.  Mention upcoming
POSIX changes re tm_gmtoff and tm_zone.  Shorten some citations
when year will do.  Shorten tz-link title.  Proper POSIX tar
format actually started in 2022a, not 1999g.  Mention SOFA license.
* NEWS: Reword and add a "Briefly".
 Makefile     |  5 ++--
 NEWS         | 18 +++++++----
 newctime.3   |  5 ++--
 theory.html  | 26 ++++++++--------
 tz-art.html  |  2 +-
 tz-link.html | 85 +++++++++++++++++++++++++---------------------------
 tzfile.5     |  2 +-
 7 files changed, 75 insertions(+), 68 deletions(-)

diff --git a/Makefile b/Makefile
index ae0f3fd8..b68f843d 100644
--- a/Makefile
+++ b/Makefile
@@ -298,8 +298,9 @@ GCC_DEBUG_FLAGS = -DGCC_LINT -g3 -O3 -fno-common \
 # guess TM_GMTOFF from other macros; define NO_TM_GMTOFF to suppress this.
 # Similarly, if your system has a "zone abbreviation" field, define
 #	-DTM_ZONE=tm_zone
-# and define NO_TM_ZONE to suppress any guessing.  These two fields are not
-# required by POSIX, but are widely available on GNU/Linux and BSD systems.
+# and define NO_TM_ZONE to suppress any guessing.  Although these two fields
+# not required by POSIX, a future version of POSIX is planned to require them
+# and they are widely available on GNU/Linux and BSD systems.
 # The next batch of options control support for external variables
 # exported by tzcode.  In practice these variables are less useful
diff --git a/NEWS b/NEWS
index 4c1c48dc..e5c20673 100644
--- a/NEWS
+++ b/NEWS
@@ -2,20 +2,26 @@ News for the tz database
 Unreleased, experimental changes
+  Briefly:
+    Work around awk bug in FreeBSD, macOS, etc.
+    Improve tzselect on intercontinental Zones.
   Changes to code
-    Work around a bug in macOS 'awk' that broke commands like 'make
-    traditional_tarballs'.  (Problem reported by Deborah Goldsmith.)
+    Work around a bug in onetrueawk that broke commands like
+    'make traditional_tarballs' on FreeBSD, macOS, etc.
+    (Problem reported by Deborah Goldsmith.)
-    Add structured comments to zone1970.tab that clarify whether Zones
-    like Europe/Istanbul cross continent or ocean boundaries.
+    Add code to tzselect that uses experimental structured comments in
+    zone1970.tab to clarify whether Zones like Africa/Abidjan and
+    Europe/Istanbul cross continent or ocean boundaries.
     (Inspired by a problem reported by Peter Krefting.)
     Fix bug with 'zic -d /a/b/c' when /a is unwritable but the
     directory /a/b already exists.
-    The script zoneinfo2tdf.pl has been removed, as it was unused and
-    triggered false malware alarms on some email servers.
+    Remove zoneinfo2tdf.pl, as it was unused and triggered false
+    malware alarms on some email servers.
 Release 2022b - 2022-08-10 15:38:32 -0700
diff --git a/newctime.3 b/newctime.3
index 1b1790fd..86615498 100644
--- a/newctime.3
+++ b/newctime.3
@@ -271,8 +271,9 @@ so were made when the library containing these functions was
 Similarly, the
 .B tzname
-variable is optional.
-There is no guarantee that these fields and this variable will
+variable is optional; also, there is no guarantee that
+.B tzname
 continue to exist in this form in future releases of this code.
 .ta \w'/usr/share/zoneinfo/posixrules\0\0'u
diff --git a/theory.html b/theory.html
index 2b14c511..56390ae4 100644
--- a/theory.html
+++ b/theory.html
@@ -122,7 +122,7 @@ If geolocation information is available, a selection interface can
 locate the user on a timezone map or prioritize names that are
 geographically close. For an example selection interface, see the
 <code>tzselect</code> program in the <code><abbr>tz</abbr></code> code.
-The <a href="http://cldr.unicode.org">Unicode Common Locale Data
+The <a href="https://cldr.unicode.org">Unicode Common Locale Data
 Repository</a> contains data that may be useful for other selection
 interfaces; it maps timezone names like <code>Europe/Prague</code> to
 locale-dependent strings like "Prague", "Praha", "Прага", and "布拉格".
@@ -571,7 +571,7 @@ in decreasing order of importance:
     locations while uninhabited.
     The leading '<code>-</code>' is a flag that the <abbr>UT</abbr> offset is in
     some sense undefined; this notation is derived
-    from <a href="https://tools.ietf.org/html/rfc3339">Internet
+    from <a href="https://datatracker.ietf.org/doc/html/rfc3339">Internet
     <abbr title="Request For Comments">RFC</abbr> 3339</a>.
@@ -624,7 +624,7 @@ Errors in the <code><abbr>tz</abbr></code> database arise from many sources:
     should be observed.
     In her 2015 book
-    href="http://www.hup.harvard.edu/catalog.php?isbn=9780674286146">The
+    href="https://www.hup.harvard.edu/catalog.php?isbn=9780674286146">The
     Global Transformation of Time, 1870–1950</a></cite>,
     Vanessa Ogle writes
     "Outside of Europe and North America there was no system of time
@@ -810,7 +810,7 @@ href="https://www.dissentmagazine.org/blog/booked-a-global-history-of-time-vanes
     See: Stephenson FR, Morrison LV, Hohenkerk CY.
     <a href="https://dx.doi.org/10.1098/rspa.2016.0404">Measurement of
     the Earth's rotation: 720 BC to AD 2015</a>.
-    <cite>Proc Royal Soc A</cite>. 2016 Dec 7;472:20160404.
+    <cite>Proc Royal Soc A</cite>. 2016;472:20160404.
     Also see: Espenak F. <a
     in Delta T (ΔT)</a>.
@@ -1036,7 +1036,7 @@ an older <code>zic</code>.
     and numeric data as described <a href="#POSIX">above</a>.
     The file's format is <dfn><abbr>TZif</abbr></dfn>,
     a timezone information format that contains binary data; see
-    <a href="https://tools.ietf.org/html/8536">Internet
+    <a href="https://datatracker.ietf.org/doc/html/8536">Internet
     <abbr>RFC</abbr> 8536</a>.
     The daylight saving time rules to be used for a
     particular timezone are encoded in the
@@ -1064,11 +1064,12 @@ an older <code>zic</code>.
     The code supports platforms with a <abbr>UT</abbr> offset member
-    in <code>struct tm</code>, e.g., <code>tm_gmtoff</code>.
-  </li>
-  <li>
-    The code supports platforms with a time zone abbreviation member in
-    <code>struct tm</code>, e.g., <code>tm_zone</code>.
+    in <code>struct tm</code>, e.g., <code>tm_gmtoff</code>,
+    or with a time zone abbreviation member in
+    <code>struct tm</code>, e.g., <code>tm_zone</code>. As noted
+    in <a href="https://austingroupbugs.net/view.php?id=1533">Austin
+    Group defect 1533</a>, a future version of POSIX is planned to
+    require <code>tm_gmtoff</code> and <code>tm_zone</code>.
     Functions <code>tzalloc</code>, <code>tzfree</code>,
@@ -1129,7 +1130,8 @@ The vestigial <abbr>API</abbr>s are:
     Although it can still be used in arguments to
     <code>mktime</code> to disambiguate timestamps near
-    a <abbr>DST</abbr> transition when the clock jumps back, this
+    a <abbr>DST</abbr> transition when the clock jumps back on
+    platforms lacking <code>tm_gmtoff</code>, this
     disambiguation does not work when standard time itself jumps back,
     which can occur when a location changes to a time zone with a
     lesser <abbr>UT</abbr> offset.
@@ -1277,7 +1279,7 @@ the operating system kernel clock as described in
 <a href="tz-link.html#precision">Precision timekeeping</a>,
 and this package by default installs a <samp>leapseconds</samp> file
 commonly used by
-<a href="http://www.ntp.org"><abbr title="Network Time Protocol">NTP</abbr></a>
+<a href="https://www.ntp.org"><abbr title="Network Time Protocol">NTP</abbr></a>
 software that adjusts the kernel clock.
 However, kernel-clock twiddling approximates UTC only roughly,
 and systems needing more-precise UTC can use this package's leap
diff --git a/tz-art.html b/tz-art.html
index f1bd4c57..56795341 100644
--- a/tz-art.html
+++ b/tz-art.html
@@ -621,7 +621,7 @@ but maybe in your time zone I haven't finished yet. So stay tuned!"
 <h2>See also</h2>
-<li><a href="tz-link.html">Sources for Time Zone and Daylight Saving
+<li><a href="tz-link.html">Time Zone and Daylight Saving
 Time Data</a></li>
diff --git a/tz-link.html b/tz-link.html
index 25320694..d3b37664 100644
--- a/tz-link.html
+++ b/tz-link.html
@@ -1,14 +1,14 @@
 <!DOCTYPE html>
 <html lang="en">
-<title>Sources for time zone and daylight saving time data</title>
+<title>Time zone and daylight saving time data</title>
 <meta charset="UTF-8">
 pre {margin-left: 2em; white-space: pre-wrap;}
-<h1>Sources for time zone and daylight saving time data</h1>
+<h1>Time zone and daylight saving time data</h1>
 <a href="https://en.wikipedia.org/wiki/Time_zone">Time zone</a> and
 <a href="https://en.wikipedia.org/wiki/Daylight_saving_time">daylight-saving</a>
@@ -52,9 +52,9 @@ area.
 	  <li><a href="#costs">Costs and benefits of time shifts</a></li>
 	  <li><a href="#precision">Precision timekeeping</a></li>
 	  <li><a href="#notation">Time notation</a></li>
-	  <li><a href="#see-also">See also</a></li>
+      <li><a href="#see-also">See also</a></li>
@@ -80,7 +80,7 @@ C Library</a> (used in
 title="Berkeley Software Distribution">BSD</abbr></a>,
 <a href="https://netbsd.org">Net<abbr>BSD</abbr></a>,
 <a href="https://www.openbsd.org">Open<abbr>BSD</abbr></a>,
-<a href="https://www.chromium.org/chromium-os">Chromium OS</a>,
+<a href="https://www.chromium.org/chromium-os/">Chromium OS</a>,
 <a href="https://cygwin.com">Cygwin</a>,
 <a href="https://mariadb.org">MariaDB</a>,
 <a href="https://en.wikipedia.org/wiki/MINIX">MINIX</a>,
@@ -166,7 +166,7 @@ Since 1996, each version has been a four-digit year followed by
 lower-case letter (<samp>a</samp> through <samp>z</samp>,
 then <samp>za</samp> through <samp>zz</samp>, then <samp>zza</samp>
 through <samp>zzz</samp>, and so on).
-Since version 1999g, each release has been distributed in
+Since version 2022a, each release has been distributed in
 <a href="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92_13_06">POSIX
 ustar interchange format</a>, compressed as described above;
 older releases use a nearly-compatible format.
@@ -192,7 +192,7 @@ After obtaining the code and data files, see the
 The code lets you compile the <code><abbr>tz</abbr></code> source files into
 machine-readable binary files, one for each location. The binary files
 are in a special timezone information format (<dfn><abbr>TZif</abbr></dfn>)
-specified by <a href="https://tools.ietf.org/html/8536">Internet
+specified by <a href="https://datatracker.ietf.org/doc/html/8536">Internet
 <abbr>RFC</abbr> 8536</a>.
 The code also lets
 you read a <abbr>TZif</abbr> file and interpret timestamps for that
@@ -276,7 +276,7 @@ Studio Code</a>.
 For further information about updates, please see
-<a href="https://tools.ietf.org/html/rfc6557">Procedures for
+<a href="https://datatracker.ietf.org/doc/html/rfc6557">Procedures for
 Maintaining the Time Zone Database</a> (Internet <abbr
 title="Request For Comments">RFC</abbr> 6557). More detail can be
 found in <a href="theory.html">Theory and pragmatics of the
@@ -327,10 +327,8 @@ title="Structured Query Language">SQL</abbr></a> form.</li>
 href="https://twiki.org/cgi-bin/xtra/tzdatepick.html">Date and Time Gateway</a>
 lets you see the <code><abbr>TZ</abbr></code> values directly.</li>
 Time in 1000 Places</a> uses descriptions of the values.</li>
-<li><a href="https://timezoneconverterapp.com/">Time Zone Converter</a>
-uses a pulldown menu.</li>
 <li><a href="https://home.kpn.nl/vanadovv/time/TZworld.html">Complete
 timezone information for all countries</a>
 displays tables of <abbr>DST</abbr> rules.
@@ -340,8 +338,8 @@ Worldwide</a> lets you sort zone names and convert times.</li>
 time map and a time converter.</li>
 <li><a href="https://www.zeitverschiebung.net/en/">Time Difference</a>
 calculates the current time difference between locations.</li>
-<li><a href="http://www.wx-now.com">Weather Now</a> and
-<a href="http://www.thetimenow.com">The Time Now</a> list the weather too.</li>
+<li><a href="https://www.wx-now.com">Weather Now</a> and
+<a href="https://www.thetimenow.com">The Time Now</a> list the weather too.</li>
@@ -351,26 +349,26 @@ calculates the current time difference between locations.</li>
 <li>The <a href="https://www.ietf.org">Internet Engineering Task Force</a>'s
 <a href="https://datatracker.ietf.org/wg/tzdist/charter/">Time Zone Data
 Distribution Service (tzdist) working group</a> defined <a
 (Internet <abbr>RFC</abbr> 7808), a time zone data distribution service,
-along with <a href="https://tools.ietf.org/html/rfc7809">CalDAV</a>
+along with <a href="https://datatracker.ietf.org/doc/html/rfc7809">CalDAV</a>
 (Internet <abbr>RFC</abbr> 7809), a calendar access protocol for
 transferring time zone data by reference.
 <a href="https://devguide.calconnect.org/Time-Zones/TZDS/">TZDIST
 implementations</a> are available.
 The <a href="https://www.ietf.org/mailman/listinfo/tzdist-bis">tzdist-bis
 mailing list</a> discusses possible extensions.</li>
-<li>The <a href="https://tools.ietf.org/html/rfc5545">
+<li>The <a href="https://datatracker.ietf.org/doc/html/rfc5545">
 Internet Calendaring and Scheduling Core Object Specification
 (iCalendar)</a> (Internet <abbr>RFC</abbr> 5445)
 covers time zone
 data; see its VTIMEZONE calendar component.
 The iCalendar format requires specialized parsers and generators; a
-variant <a href="https://tools.ietf.org/html/rfc6321">xCal</a>
+variant <a href="https://datatracker.ietf.org/doc/html/rfc6321">xCal</a>
 (Internet <abbr>RFC</abbr> 6321) uses
 <a href="https://www.w3.org/XML/"><abbr
 title="Extensible Markup Language">XML</abbr></a> format, and a variant
-<a href="https://tools.ietf.org/html/rfc7265">jCal</a>
+<a href="https://datatracker.ietf.org/doc/html/rfc7265">jCal</a>
 (Internet <abbr>RFC</abbr> 7265)
 uses <a href="https://www.json.org"><abbr
 title="JavaScript Object Notation">JSON</abbr></a> format.</li>
@@ -413,13 +411,13 @@ transition in the <code><abbr>tz</abbr></code> database.</li>
 Database Parser</a> is a
 <a href="https://en.wikipedia.org/wiki/C%2B%2B">C++</a> parser and
 runtime library with <a
 adopted by
 <a href="https://en.wikipedia.org/wiki/C++20">C++20</a>,
 the current iteration of the C++ standard.
 It is freely available under the
 <abbr title="Massachusetts Institute of Technology">MIT</abbr> license.</li>
-<li><a id="ICU" href="http://site.icu-project.org">International Components for
+<li><a id="ICU" href="https://icu.unicode.org">International Components for
 Unicode (<abbr>ICU</abbr>)</a> contains C/C++ and <a
 libraries for internationalization that
@@ -549,7 +547,7 @@ Ruby Timezone Library</a>
 compiles <code><abbr>tz</abbr></code> source into
 <a href="https://www.ruby-lang.org/en/">Ruby</a>.
 It is freely available under the <abbr>MIT</abbr> license.</li>
-<li>The <a href="http://www.squeaksource.com/Chronos/">Chronos Date/Time
+<li>The <a href="https://www.squeaksource.com/Chronos/">Chronos Date/Time
 Library</a> is
 a <a href="https://en.wikipedia.org/wiki/Smalltalk">Smalltalk</a> class
 library that compiles <code><abbr>tz</abbr></code> source into a time
@@ -798,7 +796,7 @@ political subdivision data related to time zones.</li>
 <li><a href="https://home.kpn.nl/vanadovv/time/Multizones.html">Time
 zone boundaries for multizone countries</a> summarizes legal
 boundaries between time zones within countries.</li>
-<li><a href="http://manifold.net/info/freestuff.shtml">Manifold Software
+<li><a href="https://manifold.net/info/freestuff.shtml">Manifold Software
 – GIS and Database Tools</a> includes a Manifold-format map of
 world time zone boundaries distributed under the
@@ -895,7 +893,7 @@ hreflang="he">announcements (in Hebrew)</a>.</dd>
 <dd>The Investigation and Analysis Service of the Mexican Library of
 Congress has published a <a
 hreflang="es">history of Mexican local time (in Spanish)</a>.</dd>
 <dd><a href="https://www.staff.science.uu.nl/~gent0113/wettijd/wettijd.htm"
@@ -926,7 +924,7 @@ Time Zone Proceedings</a> lists changes to time zone boundaries.</dd>
 <dd>The Oceanography, Hydrography, and Meteorology Service of the Uruguayan
 Navy (SOHMA) publishes an annual <a
-href="http://sohma.armada.mil.uy/index.php/servicios/datos-astronomicos" hreflang="es">almanac
+href="https://sohma.armada.mil.uy/index.php/servicios/datos-astronomicos" hreflang="es">almanac
 (in Spanish)</a>.</dd>
@@ -947,9 +945,9 @@ This reviews research literature and concludes that the evidence
 neither supports nor refutes road safety benefits from
 shifts in time zones.</li>
 <li>Havranek T, Herman D, Irsova D.
-<a href="https://www.econstor.eu/handle/10419/174191">Does daylight
-saving save electricity? A meta-analysis</a>. <em>Energy J.</em>
+<a href="https://www.iaee.org/en/publications/ejarticle.aspx?id=3051">Does
+daylight saving save electricity? A meta-analysis.</a>
+<em>Energy J.</em> 2018;39(2):35–61.
 doi:<a href="https://doi.org/10.5547/01956574.39.2.thav">10.5547/01956574.39.2.thav</a>.
 This analyzes research literature and concludes, "Electricity savings
 are larger for countries farther away from the equator, while
@@ -961,16 +959,14 @@ an American Academy of Sleep Medicine position statement</a>.
 2020;<a href="https://doi.org/10.5664/jcsm.8780">10.5664/jcsm.8780</a>.
 This argues for permanent standard time due to health risks of both
 <abbr>DST</abbr> transitions and permanent <abbr>DST</abbr>.</li>
-<li>Roenneberg T, Winnebeck EC, Klerman EB.
-<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6692659/">Daylight
-saving time and artificial time zones – a battle between
-biological and social times</a>. <em>Front Physiol.</em> 2019;10:944.
-doi:<a href="https://doi.org/10.3389/fphys.2019.00944">10.3389/fphys.2019.00944</a>.
-This reviews evidence about the health effects of <abbr>DST</abbr>
-and concludes,
-"In summary, the scientific literature strongly argues against the
-switching between <abbr>DST</abbr> and Standard Time and even more so against
-adopting <abbr>DST</abbr> permanently."</li>
+<li>Roenneberg T, Wirz-Justice A, Skene DJ <em>et al</em>.
+<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7205184/">Why
+should we abolish Daylight Saving Time?</a>
+<em>J Biol Rhythms</em>. 2019;34(3):227–230.
+doi:<a href="https://doi.org/10.1177/0748730419854197">10.1177/0748730419854197</a>.
+This position paper of the Society for Research on Biological Rhythms
+opposes DST changes and permanent DST, and advocates that governments adopt
+"permanent Standard Time for the health and safety of their citizens".</li>
@@ -983,7 +979,7 @@ Science of Timekeeping</a> is a thorough introduction
 to the theory and practice of precision timekeeping.</li>
 <li><a href="https://doi.org/10.1007/978-3-319-59909-0">The Science of
 Time 2016</a> contains several freely-readable papers.</li>
-<li><a href="http://www.ntp.org"><abbr
+<li><a href="https://www.ntp.org"><abbr
 title="Network Time Protocol">NTP</abbr>: The Network
 Time Protocol</a> (Internet <abbr>RFC</abbr> 5905)
 discusses how to synchronize clocks of
@@ -998,7 +994,7 @@ title="Institute of Electrical and Electronics Engineers">IEEE</abbr> 1588)
 can achieve submicrosecond clock accuracy on a local area network
 with special-purpose hardware.</li>
 Options for <abbr title="Dynamic Host Configuration Protocol">DHCP</abbr></a>
 (Internet <abbr>RFC</abbr> 4833)
 specifies a <a
@@ -1012,14 +1008,15 @@ Scales</a> describes astronomical time scales like
 <abbr title="Barycentric Dynamic Time">TDB</abbr>.
 <li>The <a href="https://www.iau.org"><abbr
 title="International Astronomical Union">IAU</abbr></a>'s <a
 title="Standards Of Fundamental Astronomy">SOFA</abbr></a>
 collection contains C and <a
 code for converting among time scales like
 <abbr title="International Atomic Time">TAI</abbr>,
 <abbr>TDB</abbr>, <abbr>TDT</abbr> and
+<abbr>UTC</abbr>. It is freely available under the
+<a href="https://www.iausofa.org/tandc.html">SOFA license</a>.</li>
 href="https://www.giss.nasa.gov/tools/mars24/help/notes.html">Mars24 Sunclock
 – Time on Mars</a> describes Airy Mean Time (<abbr>AMT</abbr>) and the
@@ -1065,7 +1062,7 @@ the <abbr>NTP</abbr> reference implementation, <a
 href="https://github.com/google/unsmear">supports</a> conversion between
 <abbr>UTC</abbr> and smeared <abbr>POSIX</abbr> timestamps, and is used by major
 cloud service providers. However, according to
-<a href="https://tools.ietf.org/html/rfc8633#section-3.7.1">§3.7.1 of
+<a href="https://datatracker.ietf.org/doc/html/rfc8633#section-3.7.1">§3.7.1 of
 Network Time Protocol Best Current Practices</a>
 (Internet <abbr>RFC</abbr> 8633), leap smearing is not suitable for
 applications requiring accurate <abbr>UTC</abbr> or civil time,
@@ -1089,7 +1086,7 @@ again.</li>
 <h2 id="notation">Time notation</h2>
-<li>The <a id="CLDR" href="http://cldr.unicode.org">Unicode Common Locale Data
+<li>The <a id="CLDR" href="https://cldr.unicode.org">Unicode Common Locale Data
 Repository (<abbr>CLDR</abbr>) Project</a> has localizations for time
 zone names, abbreviations, identifiers, and formats. For example, it
 contains French translations for "Eastern European Summer Time",
@@ -1111,13 +1108,13 @@ interchange – Part 1: Basic rules</em></a>.</li>
 <a href="https://www.w3.org/TR/xmlschema/#dateTime"><abbr>XML</abbr>
 Schema: Datatypes – dateTime</a> specifies a format inspired by
 <abbr>ISO</abbr> 8601 that is in common use in <abbr>XML</abbr> data.</li>
-<li><a href="https://tools.ietf.org/html/rfc5322#section-3.3">§3.3 of
+<li><a href="https://datatracker.ietf.org/doc/html/rfc5322#section-3.3">§3.3 of
 Internet Message Format</a> (Internet <abbr>RFC</abbr> 5322)
 specifies the time notation used in email and <a
-<a href="https://tools.ietf.org/html/rfc3339">Date and Time
+<a href="https://datatracker.ietf.org/doc/html/rfc3339">Date and Time
 on the Internet: Timestamps</a> (Internet <abbr>RFC</abbr> 3339)
 specifies an <abbr>ISO</abbr> 8601
 profile for use in new Internet
diff --git a/tzfile.5 b/tzfile.5
index 550b31de..280e8d8a 100644
--- a/tzfile.5
+++ b/tzfile.5
@@ -486,7 +486,7 @@ of one hour, or of 15 minutes, or of 1 minute.
 Olson A, Eggert P, Murchison K. The Time Zone Information Format (TZif).
 2019 Feb.
-.UR https://\:www.rfc-editor.org/\:info/\:rfc8536
+.UR https://\:datatracker.ietf.org/\:doc/\:html/\:rfc8536
 Internet RFC 8536
 .UR https://\:doi.org/\:10.17487/\:RFC8536

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