Squashed 'tz/' changes from d2c79c4bc..e6150f292

95ecc37d2 Release 2022a
d90452ece * NEWS: Add 2022a "Briefly".
44b73f770 * NEWS: Coalesce Palestine entries.
049044d77 * zdump.c: Fix date typo in comment.
e8681e760 Adjust Chile LMT; expand 1946/1947 commentary
0caefb646 Revert "Chile’s Magallanes was like Santiago in 1946/7"
22a2dca72 URL housekeeping
6d6a21f59 Chile’s Magallanes was like Santiago in 1946/7
f4b156691 Palestine springs forward a day later
cac76bf92 Fix white space.
318759658 Add URLs to Morocco commentary (thanks to Milamber)
6ff7b3502 Fix French typo
88d2c3909 Fix Lubumbashi between 1897 and 1929
7f60edb1d * private.h (UNINIT_TRAP): Add comment.
db9347fbb Fix processing of TZif truncation
df4699ddf Add comments on Russia in 1981 (thanks to Alois Treindl)
4117b20d0 Simplify Ukraine metadata
93dcac0c6 Ukraine’s 1992/1996 DST changes 02:00s not 01:00u
b74f54452 dumptime’s argument is always nonnull now
3a11c9cc2 I18nize zdump a bit better
a12823400 Improve doc for some source files
0b8077257 Simplify recent zdump port
80096e016 zdump ports better to odd C11 platforms
b6f92f762 zdump -v reports localtime+gmtime failures better
e3c58df90 * Makefile (AWK): Warn re mawk 1.3.3 (thanks to Jonathan Ben Avraham)
9c8cb5d76 No leap second on 2022-06-30
cec7d9e2e Improve rearguard port of post-2087 Morocco
01eeac6b0 zic: omit parens that the C standard doesn’t allow
6cfaa796e Fix "el ds" typo in man pages
aa9c4662f * CONTRIBUTING: Move pull request insns to start.
4292b9320 Convert CONTRIBUTING back to plain text
b0c24fad4 Rename CONTRIBUTING.md back to CONTRIBUTING
7a200f2b3 Fix Y2242 bug in tzdb tarball generation
5f6467141 Support busybox awk
8407d785a Port zic to Solaris 10 automounts
b10ff6d60 Port tzselect to Solaris 10 /bin/sh
e4a46da99 Simplify tzselect by omitting old Bash workaround
ee44afb40 Distribute tarballs in ustar rather than gnu form
68b99887d Remove duplicate Trinidad and Tobago comment
f6c9f51fa Fix minor formatting inconsistencies
3fdd3c482 Rename CONTRIBUTING to CONTRIBUTING.md
b0de1570e Switch to Markdown format
228a93f75 Remove bad backzone link for US Virgin Is
8b409e22d Be more generous when dealing with v1 data
e5a4add00 Fix uninitialized variable bug
1a4a7eab6 spelling fix
0b13c6b41 Update Palestine commentary
59467e337 Improve Palestine predictions for 2025 and later
b102002e5 Release 2021e
d86edaf12 Palestine falls back October 29 01:00.
8da2e33e0 Palestine falls back October 28 24:00
4de3d7f24 Release 2021d
951b4f301 * NEWS: Reformat to fit in fewer columns.
5f06f9a31 zic -r now uses -00 for unspecified timestamps
f8c660ce6 Simplify zic writezone slightly
bdeb83438 Document that -00 means local time is unspecified
f74940d96 Fiji suspends DST for the 2021/2022 season
0bf5a761f Fix zic.8 typos
868ba546b Correct spelling of "Treindl" (thanks to Steffen Nurpmeso)
e5d72c0f9 Clarify comments re Rome in April 1944

git-subtree-dir: tz
git-subtree-split: e6150f292f19c33ae136f70464d6075c41a1a5f3

1 files changed, 21 insertions, 6 deletions

diff --git a/theory.html b/theory.html
index 5a05f4b..28cc88e 100644
--- a/theory.html
+++ b/theory.html
@@ -296,7 +296,7 @@ in decreasing order of importance:
   </li>
   <li>
     If a name is changed, put its old spelling in the
-    '<code>backward</code>' file.
+    '<code>backward</code>' file as a link to the new spelling.
     This means old spellings will continue to work.
     Ordinarily a name change should occur only in the rare case when
     a location's consensus English-language spelling changes; for example,
@@ -348,22 +348,37 @@ timestamps correctly and it increased maintenance burden.
 </ul>
 
 <p>
-The file '<code>zone1970.tab</code>' lists geographical locations used
+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
+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.
+The backward-compatibility file <code>zone.tab</code> is similar
+but conforms to the older-version guidelines related to <abbr>ISO</abbr> 3166-1;
+it lists only one country code per entry and unlike <code>zone1970.tab</code>
+it can list names defined in <code>backward</code>.
 </p>
 
 <p>
-Excluding '<code>backward</code>' should not affect the other data.
-If '<code>backward</code>' is excluded, excluding
-'<code>etcetera</code>' should not affect the remaining data.
+The database defines each timezone name to be a zone, or a link to a zone.
+The source file <code>backward</code> defines links for backward
+compatibility; it does not define zones.
+Although <code>backward</code> was originally designed to be optional,
+nowadays distributions typically use it
+and no great weight should be attached to whether a link
+is defined in <code>backward</code> or in some other file.
+The source file <code>etcetera</code> defines names that may be useful
+on platforms that do not support POSIX-style <code>TZ</code> strings;
+no other source file other than <code>backward</code>
+contains links to its zones.
+One of <code>etcetera</code>'s names is <code>GMT</code>,
+used by functions like <code>gmtime</code> to obtain leap
+second information on platforms that support leap seconds.
 </p>
 </section>