Import tzdata 2019a.

Approved by:	so
Security:	FreeBSD-EN-19:08.tzdata

14 files changed, 203 insertions, 65 deletions

diff --git a/contrib/tzdata/Makefile b/contrib/tzdata/Makefile
index d8d8e21..25f1d35 100644
--- a/contrib/tzdata/Makefile
+++ b/contrib/tzdata/Makefile
@@ -12,7 +12,10 @@ VERSION=	unknown
 # Email address for bug reports.
 BUGEMAIL=	tz@iana.org
 
-# Choose source data features.  To get new features right away, use:
+# DATAFORM selects the data format.
+# Available formats represent essentially the same data, albeit
+# possibly with minor discrepancies that users are not likely to notice.
+# To get new features and the best data right away, use:
 #	DATAFORM=	vanguard
 # To wait a while before using new features, to give downstream users
 # time to upgrade zic (the default), use:
@@ -33,11 +36,11 @@ DATAFORM=		main
 LOCALTIME=	GMT
 
 # If you want something other than Eastern United States time as a template
-# for handling POSIX-style timezone environment variables,
+# for handling ruleless POSIX-style timezone environment variables,
 # change the line below (after finding the timezone you want in the
 # one of the $(TDATA) source files, or adding it to a source file).
-# When a POSIX-style environment variable is handled, the rules in the
-# template file are used to determine "spring forward" and "fall back" days and
+# A ruleless environment setting like TZ='CST6CDT' uses the rules in the
+# template file to determine "spring forward" and "fall back" days and
 # times; the environment variable itself specifies UT offsets of standard and
 # daylight saving time.
 # Alternatively, if you discover you've got the wrong timezone, you can just
@@ -46,7 +49,6 @@ LOCALTIME=	GMT
 # Use the command
 #	make zonenames
 # to get a list of the values you can use for POSIXRULES.
-# If you want POSIX compatibility, use "America/New_York".
 
 POSIXRULES=	America/New_York
 
@@ -113,8 +115,8 @@ TIME_T_ALTERNATIVES = $(TIME_T_ALTERNATIVES_HEAD) $(TIME_T_ALTERNATIVES_TAIL)
 TIME_T_ALTERNATIVES_HEAD = int64_t
 TIME_T_ALTERNATIVES_TAIL = int32_t uint32_t uint64_t
 
-# What kind of TZif data files to generate.
-# (TZif is the binary time zone data format that zic generates.)
+# What kind of TZif data files to generate.  (TZif is the binary time
+# zone data format that zic generates; see Internet RFC 8536.)
 # If you want only POSIX time, with time values interpreted as
 # seconds since the epoch (not counting leap seconds), use
 #	REDO=		posix_only
@@ -360,6 +362,9 @@ LEAPSECONDS=
 zic=		./zic
 ZIC=		$(zic) $(ZFLAGS)
 
+# To shrink the size of installed TZif files,
+# append "-r @N" to omit data before N-seconds-after-the-Epoch.
+# See the zic man page for more about -r.
 ZFLAGS=
 
 # How to use zic to install TZif files.
@@ -491,7 +496,8 @@ MANTXTS=	newctime.3.txt newstrftime.3.txt newtzset.3.txt \
 COMMON=		calendars CONTRIBUTING LICENSE Makefile \
 			NEWS README theory.html version
 WEB_PAGES=	tz-art.html tz-how-to.html tz-link.html
-CHECK_WEB_PAGES=check_tz-art.html check_tz-how-to.html check_tz-link.html
+CHECK_WEB_PAGES=check_theory.html check_tz-art.html \
+			check_tz-how-to.html check_tz-link.html
 DOCS=		$(MANS) date.1 $(MANTXTS) $(WEB_PAGES)
 PRIMARY_YDATA=	africa antarctica asia australasia \
 		europe northamerica southamerica
@@ -804,9 +810,10 @@ check_tzs:	$(TZS) $(TZS_NEW)
 		touch $@
 
 check_web:	$(CHECK_WEB_PAGES)
+check_theory.html: theory.html
 check_tz-art.html: tz-art.html
 check_tz-link.html: tz-link.html
-check_tz-art.html check_tz-link.html:
+check_theory.html check_tz-art.html check_tz-link.html:
 		$(CURL) -sS --url https://validator.w3.org/nu/ -F out=gnu \
 		    -F file=@$$(expr $@ : 'check_\(.*\)') -o $@.out && \
 		  test ! -s $@.out || { cat $@.out; exit 1; }
@@ -840,11 +847,13 @@ check_zishrink_posix check_zishrink_right: \
 		touch $@
 
 clean_misc:
+		rm -fr check_*.dir
 		rm -f *.o *.out $(TIME_T_ALTERNATIVES) \
 		  check_* core typecheck_* \
 		  date tzselect version.h zdump zic yearistype libtz.a
 clean:		clean_misc
-		rm -fr *.dir *.zi tzdb-*/ $(TZS_NEW)
+		rm -fr *.dir tzdb-*/
+		rm -f *.zi $(TZS_NEW)
 
 maintainer-clean: clean
 		@echo 'This command is intended for maintainers to use; it'
diff --git a/contrib/tzdata/NEWS b/contrib/tzdata/NEWS
index 37f2281..9d0e9c0 100644
--- a/contrib/tzdata/NEWS
+++ b/contrib/tzdata/NEWS
@@ -1,5 +1,53 @@
 News for the tz database
 
+Release 20198 - 2019-03-25 22:01:33 -0700
+
+  Briefly:
+    Palestine "springs forward" on 2019-03-30 instead of 2019-03-23.
+    Metlakatla "fell back" to rejoin Alaska Time on 2019-01-20 at 02:00.
+
+  Changes to past and future timestamps
+
+    Palestine will not start DST until 2019-03-30, instead of 2019-03-23 as
+    previously predicted.  Adjust our prediction by guessing that spring
+    transitions will be between 24 and 30 March, which matches recent practice
+    since 2016.  (Thanks to Even Scharning and Tim Parenti.)
+
+    Metlakatla ended its observance of Pacific standard time,
+    rejoining Alaska Time, on 2019-01-20 at 02:00.  (Thanks to Ryan
+    Stanley and Tim Parenti.)
+
+  Changes to past timestamps
+
+    Israel observed DST in 1980 (08-02/09-13) and 1984 (05-05/08-25).
+    (Thanks to Alois Treindl and Isaac Starkman.)
+
+  Changes to time zone abbreviations
+
+    Etc/UCT is now a backward-compatibility link to Etc/UTC, instead
+    of being a separate zone that generates the abbreviation "UCT",
+    which nowadays is typically a typo.  (Problem reported by Isiah
+    Meadows.)
+
+  Changes to code
+
+    zic now has an -r option to limit the time range of output data.
+    For example, 'zic -r @1000000000' limits the output data to
+    timestamps starting 1000000000 seconds after the Epoch.
+    This helps shrink output size and can be useful for applications
+    not needing the full timestamp history, such as TZDIST truncation;
+    see Internet RFC 8536 section 5.1.  (Inspired by a feature request
+    from Christopher Wong, helped along by bug reports from Wong and
+    from Tim Parenti.)
+
+  Changes to documentation
+
+    Mention Internet RFC 8536 (February 2019), which documents TZif.
+
+    tz-link.html now cites tzdata-meta
+    <https://tzdata-meta.timtimeonline.com/>.
+
+
 Release 2018i - 2018-12-30 11:05:43 -0800
 
   Briefly:
@@ -400,8 +448,9 @@ Release 2018d - 2018-03-22 07:05:46 -0700
       downstream parsers do not support it.
 
     * The build procedure constructs three files vanguard.zi, main.zi,
-      and rearguard.zi, one for each format.  The files represent the
-      same data as closely as the formats allow.  These three files
+      and rearguard.zi, one for each format.  Although the files
+      represent essentially the same data, they may have minor
+      discrepancies that users are not likely to notice.  The files
       are intended for downstream data consumers and are not
       installed.  Zoneinfo parsers that do not support negative SAVE values
       should start using rearguard.zi, so that they will be unaffected
diff --git a/contrib/tzdata/README b/contrib/tzdata/README
index efe7a17..dd6fcf7 100644
--- a/contrib/tzdata/README
+++ b/contrib/tzdata/README
@@ -1,7 +1,7 @@
 README for the tz distribution
 
-"What time is it?" -- Richard Deacon as The King
-"Any time you want it to be." -- Frank Baxter as The Scientist
+"Where do I set the hands of the clock?" -- Les Tremayne as The King
+"Oh that--you can set them any place you want." -- Frank Baxter as The Scientist
 					(from the Bell System film "About Time")
 
 The Time Zone Database (called tz, tzdb or zoneinfo) contains code and
diff --git a/contrib/tzdata/africa b/contrib/tzdata/africa
index 0a0f586..a58c11c 100644
--- a/contrib/tzdata/africa
+++ b/contrib/tzdata/africa
@@ -364,6 +364,11 @@ Zone	Africa/Cairo	2:05:09 -	LMT	1900 Oct
 # See Africa/Lagos.
 
 # Eritrea
+# See Africa/Nairobi.
+
+# Eswatini (formerly Swaziland)
+# See Africa/Johannesburg.
+
 # Ethiopia
 # See Africa/Nairobi.
 #
@@ -1188,7 +1193,7 @@ Zone Africa/Johannesburg 1:52:00 -	LMT	1892 Feb 8
 			1:30	-	SAST	1903 Mar
 			2:00	SA	SAST
 Link Africa/Johannesburg Africa/Maseru	   # Lesotho
-Link Africa/Johannesburg Africa/Mbabane    # Swaziland
+Link Africa/Johannesburg Africa/Mbabane    # Eswatini
 #
 # Marion and Prince Edward Is
 # scientific station since 1947
@@ -1230,9 +1235,6 @@ Zone	Africa/Juba	2:06:28 -	LMT	1931
 			2:00	Sudan	CA%sT	2000 Jan 15 12:00
 			3:00	-	EAT
 
-# Swaziland
-# See Africa/Johannesburg.
-
 # Tanzania
 # See Africa/Nairobi.
 
diff --git a/contrib/tzdata/asia b/contrib/tzdata/asia
index 3165203..d790da5 100644
--- a/contrib/tzdata/asia
+++ b/contrib/tzdata/asia
@@ -1620,6 +1620,24 @@ Rule	Zion	1974	only	-	Jul	 7	0:00	1:00	D
 Rule	Zion	1974	only	-	Oct	13	0:00	0	S
 Rule	Zion	1975	only	-	Apr	20	0:00	1:00	D
 Rule	Zion	1975	only	-	Aug	31	0:00	0	S
+
+# From Alois Treindl (2019-03-06):
+# http://www.moin.gov.il/Documents/שעון קיץ/clock-50-years-7-2014.pdf
+# From Isaac Starkman (2019-03-06):
+# Summer time was in that period in 1980 and 1984, see
+# https://www.ynet.co.il/articles/0,7340,L-3951073,00.html
+# You can of course read it in translation.
+# I checked the local newspapers for that years.
+# It started on midnight and end at 01.00 am.
+# From Paul Eggert (2019-03-06):
+# Also see this thread about the moin.gov.il URL:
+# https://mm.icann.org/pipermail/tz/2018-November/027194.html
+Rule	Zion	1980	only	-	Aug	 2	0:00	1:00	D
+Rule	Zion	1980	only	-	Sep	13	1:00	0	S
+Rule	Zion	1984	only	-	May	 5	0:00	1:00	D
+Rule	Zion	1984	only	-	Aug	25	1:00	0	S
+
+# From Shanks & Pottenger:
 Rule	Zion	1985	only	-	Apr	14	0:00	1:00	D
 Rule	Zion	1985	only	-	Sep	15	0:00	0	S
 Rule	Zion	1986	only	-	May	18	0:00	1:00	D
@@ -3071,9 +3089,15 @@ Zone	Asia/Karachi	4:28:12 -	LMT	1907
 # the official website, though the decree did not specify the exact
 # time of the time shift.
 # http://www.palestinecabinet.gov.ps/Website/AR/NDecrees/ViewFile.ashx?ID=e7a42ab7-ee23-435a-b9c8-a4f7e81f3817
+
+# From Even Scharning (2019-03-23):
+# DST in Palestine will start on 30 March this year, not 23 March as the time
+# zone database predicted.
+# https://ramallah.news/post/123610
 #
-# From Paul Eggert (2018-03-16):
-# For 2016 on, predict spring transitions on March's fourth Saturday at 01:00.
+# From Tim Parenti (2019-03-23):
+# Combining this with the rules observed since 2016, adjust our spring
+# transition guess to Mar Sat>=24.
 
 # Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE	LETTER/S
 Rule EgyptAsia	1957	only	-	May	10	0:00	1:00	S
@@ -3104,7 +3128,7 @@ Rule Palestine	2012	only	-	Sep	21	1:00	0	-
 Rule Palestine	2013	only	-	Sep	Fri>=21	0:00	0	-
 Rule Palestine	2014	2015	-	Oct	Fri>=21	0:00	0	-
 Rule Palestine	2015	only	-	Mar	lastFri	24:00	1:00	S
-Rule Palestine	2016	max	-	Mar	Sat>=22	1:00	1:00	S
+Rule Palestine	2016	max	-	Mar	Sat>=24	1:00	1:00	S
 Rule Palestine	2016	max	-	Oct	lastSat	1:00	0	-
 
 # Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
@@ -3596,5 +3620,17 @@ Zone Asia/Ho_Chi_Minh	7:06:40 -	LMT	1906 Jul  1
 			8:00	-	+08	1975 Jun 13
 			7:00	-	+07
 
+# From Paul Eggert (2019-02-19):
+#
+# The Ho Chi Minh entry suffices for most purposes as it agrees with all of
+# Vietnam since 1975-06-13.  Presumably clocks often changed in south Vietnam
+# in the early 1970s as locations changed hands during the war; however the
+# details are unknown and would likely be too voluminous for this database.
+#
+# For timestamps in north Vietnam back to 1970 (the tzdb cutoff),
+# use Asia/Bangkok; see the VN entries in the file zone1970.tab.
+# For timestamps before 1970, see Asia/Hanoi in the file 'backzone'.
+
+
 # Yemen
 # See Asia/Riyadh.
diff --git a/contrib/tzdata/backward b/contrib/tzdata/backward
index 51e10f4..b4ae3cf 100644
--- a/contrib/tzdata/backward
+++ b/contrib/tzdata/backward
@@ -77,6 +77,7 @@ Link	Pacific/Easter		Chile/EasterIsland
 Link	America/Havana		Cuba
 Link	Africa/Cairo		Egypt
 Link	Europe/Dublin		Eire
+Link	Etc/UTC			Etc/UCT
 Link	Europe/London		Europe/Belfast
 Link	Europe/Chisinau		Europe/Tiraspol
 Link	Europe/London		GB
@@ -111,7 +112,7 @@ Link	Asia/Taipei		ROC
 Link	Asia/Seoul		ROK
 Link	Asia/Singapore		Singapore
 Link	Europe/Istanbul		Turkey
-Link	Etc/UCT			UCT
+Link	Etc/UTC			UCT
 Link	America/Anchorage	US/Alaska
 Link	America/Adak		US/Aleutian
 Link	America/Phoenix		US/Arizona
diff --git a/contrib/tzdata/backzone b/contrib/tzdata/backzone
index 97792b1..380c492 100644
--- a/contrib/tzdata/backzone
+++ b/contrib/tzdata/backzone
@@ -204,7 +204,7 @@ Zone	Africa/Maseru	1:50:00 -	LMT	1903 Mar
 			2:00	1:00	SAST	1944 Mar 19  2:00
 			2:00	-	SAST
 
-# Swaziland
+# Eswatini (formerly Swaziland)
 Zone	Africa/Mbabane	2:04:24 -	LMT	1903 Mar
 			2:00	-	SAST
 
@@ -625,7 +625,7 @@ Zone	Europe/Sarajevo	1:13:40	-	LMT	1884
 			1:00	-	CET	1982 Nov 27
 			1:00	EU	CE%sT
 
-# Macedonia
+# North Macedonia
 Zone	Europe/Skopje	1:25:44	-	LMT	1884
 			1:00	-	CET	1941 Apr 18 23:00
 			1:00	C-Eur	CE%sT	1945 May  8  2:00s
diff --git a/contrib/tzdata/etcetera b/contrib/tzdata/etcetera
index 5d02c44..8b6bed3 100644
--- a/contrib/tzdata/etcetera
+++ b/contrib/tzdata/etcetera
@@ -19,7 +19,6 @@
 
 Zone	Etc/GMT		0	-	GMT
 Zone	Etc/UTC		0	-	UTC
-Zone	Etc/UCT		0	-	UCT
 
 # The following link uses older naming conventions,
 # but it belongs here, not in the file 'backward',
diff --git a/contrib/tzdata/europe b/contrib/tzdata/europe
index 587f7b0..b735a48 100644
--- a/contrib/tzdata/europe
+++ b/contrib/tzdata/europe
@@ -1855,7 +1855,7 @@ Zone Europe/Luxembourg	0:24:36 -	LMT	1904 Jun
 			1:00	Belgium	CE%sT	1977
 			1:00	EU	CE%sT
 
-# Macedonia
+# North Macedonia
 # See Europe/Belgrade.
 
 # Malta
@@ -3359,7 +3359,7 @@ Zone	Europe/Belgrade	1:22:00	-	LMT	1884
 Link Europe/Belgrade Europe/Ljubljana	# Slovenia
 Link Europe/Belgrade Europe/Podgorica	# Montenegro
 Link Europe/Belgrade Europe/Sarajevo	# Bosnia and Herzegovina
-Link Europe/Belgrade Europe/Skopje	# Macedonia
+Link Europe/Belgrade Europe/Skopje	# North Macedonia
 Link Europe/Belgrade Europe/Zagreb	# Croatia
 
 # Slovakia
diff --git a/contrib/tzdata/leap-seconds.list b/contrib/tzdata/leap-seconds.list
index cf54b9a..fd3d192 100644
--- a/contrib/tzdata/leap-seconds.list
+++ b/contrib/tzdata/leap-seconds.list
@@ -204,10 +204,10 @@
 #	current -- the update time stamp, the data and the name of the file
 #	will not change.
 #
-#	Updated through IERS Bulletin C56
-#	File expires on:  28 June 2019
+#	Updated through IERS Bulletin C57
+#	File expires on:  28 December 2019
 #
-#@	3770668800
+#@	3786480000
 #
 2272060800	10	# 1 Jan 1972
 2287785600	11	# 1 Jul 1972
@@ -252,4 +252,4 @@
 #	the hash line is also ignored in the
 #	computation.
 #
-#h 	62ca19f6 96a4ae0a 3708451c 9f8693f4 016604eb
+#h 	83c68138 d3650221 07dbbbcd 11fcc859 ced1106a
diff --git a/contrib/tzdata/leapseconds b/contrib/tzdata/leapseconds
index 325f3a1..886ae27 100644
--- a/contrib/tzdata/leapseconds
+++ b/contrib/tzdata/leapseconds
@@ -63,7 +63,7 @@ Leap	2016	Dec	31	23:59:60	+	S
 
 # POSIX timestamps for the data in this file:
 #updated 1467936000
-#expires 1561680000
+#expires 1577491200
 
-#	Updated through IERS Bulletin C56
-#	File expires on:  28 June 2019
+#	Updated through IERS Bulletin C57
+#	File expires on:  28 December 2019
diff --git a/contrib/tzdata/northamerica b/contrib/tzdata/northamerica
index faaf979..eee8de0 100644
--- a/contrib/tzdata/northamerica
+++ b/contrib/tzdata/northamerica
@@ -609,6 +609,15 @@ Zone America/Los_Angeles -7:52:58 -	LMT	1883 Nov 18 12:07:02
 # In a 2018-12-11 special election, Metlakatla voted to go back to
 # Alaska time (including daylight saving time) starting next year.
 # https://www.krbd.org/2018/12/12/metlakatla-to-follow-alaska-standard-time-allow-liquor-sales/
+#
+# From Ryan Stanley (2019-01-11):
+# The community will be changing back on the 20th of this month...
+# From Tim Parenti (2019-01-11):
+# Per an announcement on the Metlakatla community's official Facebook page, the
+# "fall back" will be on Sunday 2019-01-20 at 02:00:
+# https://www.facebook.com/141055983004923/photos/607150969728753/
+# So they won't be waiting for Alaska to join them on 2019-03-10, but will
+# rather change their clocks twice in seven weeks.
 
 # Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
 Zone America/Juneau	 15:02:19 -	LMT	1867 Oct 19 15:33:32
@@ -637,7 +646,7 @@ Zone America/Metlakatla	 15:13:42 -	LMT	1867 Oct 19 15:44:55
 			 -8:00	US	P%sT	1983 Oct 30  2:00
 			 -8:00	-	PST	2015 Nov  1  2:00
 			 -9:00	US	AK%sT	2018 Nov  4  2:00
-			 -8:00	-	PST	2019 Mar Sun>=8 3:00
+			 -8:00	-	PST	2019 Jan 20  2:00
 			 -9:00	US	AK%sT
 Zone America/Yakutat	 14:41:05 -	LMT	1867 Oct 19 15:12:18
 			 -9:18:55 -	LMT	1900 Aug 20 12:00
diff --git a/contrib/tzdata/theory.html b/contrib/tzdata/theory.html
index a8da065..e373022 100644
--- a/contrib/tzdata/theory.html
+++ b/contrib/tzdata/theory.html
@@ -15,7 +15,7 @@
     <ul>
       <li><a href="#scope">Scope of the <code><abbr>tz</abbr></code>
 	  database</a></li>
-      <li><a href="#naming">Names of timezones</a></li>
+      <li><a href="#naming">Timezone identifiers</a></li>
       <li><a href="#abbreviations">Time zone abbreviations</a></li>
       <li><a href="#accuracy">Accuracy of the <code><abbr>tz</abbr></code>
 	  database</a></li>
@@ -107,9 +107,9 @@ It does not always make sense to talk about a timezone's
 </section>
 
 <section>
-  <h2 id="naming">Names of timezones</h2>
+  <h2 id="naming">Timezone identifiers</h2>
 <p>
-Each timezone has a unique name.
+Each timezone has a name that uniquely identifies the timezone.
 Inexperienced users are not expected to select these names unaided.
 Distributors should provide documentation and/or a simple selection
 interface that explains each name via a map or via descriptive text like
@@ -142,10 +142,12 @@ among the following goals:
   </li>
   <li>
     Be robust in the presence of political changes.
-    For example, names of countries are ordinarily not used, to avoid
+    For example, names are typically not tied to countries, to avoid
     incompatibilities when countries change their name (e.g.,
-    Zaire&rarr;Congo) or when locations change countries (e.g., Hong
+    Swaziland&rarr;Eswatini) or when locations change countries (e.g., Hong
     Kong from UK colony to China).
+    There is no requirement that every country or national
+    capital must have a timezone name.
   </li>
   <li>
     Be portable to a wide variety of implementations.
@@ -215,19 +217,18 @@ in decreasing order of importance:
     do not need locations, since local time is not defined there.
   </li>
   <li>
-    There should typically be at least one name for each <a
-    href="https://en.wikipedia.org/wiki/ISO_3166-1"><abbr
-    title="International Organization for Standardization">ISO</abbr>
-    3166-1</a> officially assigned two-letter code for an inhabited
-    country or territory.
-  </li>
-  <li>
     If all the clocks in a timezone have agreed since 1970,
     do not bother to include more than one timezone
     even if some of the clocks disagreed before 1970.
     Otherwise these tables would become annoyingly large.
   </li>
   <li>
+    If boundaries between regions are fluid, such as during a war or
+    insurrection, do not bother to create a new timezone merely
+    because of yet another boundary change. This helps prevent table
+    bloat and simplifies maintenance.
+  </li>
+  <li>
     If a name is ambiguous, use a less ambiguous alternative;
     e.g., many cities are named San José and Georgetown, so
     prefer <code>America/Costa_Rica</code> to
@@ -299,29 +300,23 @@ in decreasing order of importance:
 </ul>
 
 <p>
-The file '<code>zone1970.tab</code>' lists geographical locations used
-to name timezones.
-It is intended to be an exhaustive list of names for geographic
-regions as described above; this is a subset of the timezones in the data.
-Although a '<code>zone1970.tab</code>' location's
-<a href="https://en.wikipedia.org/wiki/Longitude">longitude</a>
-corresponds to
-its <a href="https://en.wikipedia.org/wiki/Local_mean_time">local mean
-time (<abbr>LMT</abbr>)</a> offset with one hour for every 15&deg;
-east longitude, this relationship is not exact.
+Guidelines have evolved with time, and names following old versions of
+this guideline might not follow the current version. When guidelines
+have changed, old names continue to be supported. Guideline changes
+have included the following:
 </p>
 
-<p>
-Older versions of this package used a different naming scheme,
-and these older names are still supported.
+<ul>
+<li>
+Older versions of this package used a different naming scheme.
 See the file '<code>backward</code>' for most of these older names
 (e.g., '<code>US/Eastern</code>' instead of '<code>America/New_York</code>').
 The other old-fashioned names still supported are
 '<code>WET</code>', '<code>CET</code>', '<code>MET</code>', and
 '<code>EET</code>' (see the file '<code>europe</code>').
-</p>
+</li>
 
-<p>
+<li>
 Older versions of this package defined legacy names that are
 incompatible with the first guideline of location names, but which are
 still supported.
@@ -332,6 +327,31 @@ Also, the file '<code>backward</code>' defines the legacy names
 and the file '<code>northamerica</code>' defines the legacy names
 '<code>EST5EDT</code>', '<code>CST6CDT</code>',
 '<code>MST7MDT</code>', and '<code>PST8PDT</code>'.
+</li>
+
+<li>
+Older versions of this guideline said that
+there should typically be at least one name for each <a
+href="https://en.wikipedia.org/wiki/ISO_3166-1"><abbr
+title="International Organization for Standardization">ISO</abbr>
+3166-1</a> officially assigned two-letter code for an inhabited
+country or territory.
+This old guideline has been dropped, as it was not needed to handle
+timestamps correctly and it increased maintenance burden.
+</li>
+</ul>
+
+<p>
+The file '<code>zone1970.tab</code>' lists geographical locations used
+to name timezones.
+It is intended to be an exhaustive list of names for geographic
+regions as described above; this is a subset of the timezones in the data.
+Although a '<code>zone1970.tab</code>' location's
+<a href="https://en.wikipedia.org/wiki/Longitude">longitude</a>
+corresponds to
+its <a href="https://en.wikipedia.org/wiki/Local_mean_time">local mean
+time (<abbr>LMT</abbr>)</a> offset with one hour for every 15&deg;
+east longitude, this relationship is not exact.
 </p>
 
 <p>
@@ -983,7 +1003,9 @@ an older <code>zic</code>.
     constrained to be a string containing abbreviations
     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.
+    a timezone information format that contains binary data; see
+    <a href="https://tools.ietf.org/html/8536">Internet
+    <abbr>RFC</abbr> 8536</a>.
     The daylight saving time rules to be used for a
     particular timezone are encoded in the
     <abbr>TZif</abbr> file; the format of the file allows <abbr>US</abbr>,
@@ -1166,7 +1188,7 @@ The <code><abbr>tz</abbr></code> code and data supply the following interfaces:
 <ul>
   <li>
     A set of timezone names as per
-      "<a href="#naming">Names of timezones</a>" above.
+      "<a href="#naming">Timezone identifiers</a>" above.
   </li>
   <li>
     Library functions described in "<a href="#functions">Time and date
@@ -1213,6 +1235,17 @@ For example, users should not rely on particular <abbr>UT</abbr>
 offsets or abbreviations for timestamps, as data entries are often
 based on guesswork and these guesses may be corrected or improved.
 </p>
+
+<p>
+Timezone boundaries are not part of the stable interface.
+For example, even though the <samp>Asia/Bangkok</samp> timezone
+currently includes Chang Mai, Hanoi, and Phnom Penh, this is not part
+of the stable interface and the timezone can split at any time.
+If a calendar application records a future event in some location other
+than Bangkok by putting "<samp>Asia/Bangkok</samp>" in the event's record,
+the application should be robust in the presence of timezone splits
+between now and the future time.
+</p>
 </section>
 
 <section>
diff --git a/contrib/tzdata/version b/contrib/tzdata/version
index 63f5800..149d790 100644
--- a/contrib/tzdata/version
+++ b/contrib/tzdata/version
@@ -1 +1 @@
-2018i
+2019a