Better document the alphabetic abbreviations in use

* NEWS: Mention changes.
* southamerica (America/La_Paz):
Use BST (not BOST) for Bolivia Summer Time 1931-2.
* theory.html (Time zone abbreviations):
Document 6-char limit.  List abbreviations used.
* tz-link.htm (Time notation):
The abbreviation-removal project is done.

NEWS

@@ -9,6 +9,10 @@ Unreleased, experimental changes
     with the 'africa' and 'zone1970.tab' files.  (Problem reported by
     Michael Deckers.)
 
+    The abbreviation invented for Bolivia Summer Time (1931-2) is now
+    BST instead of BOST, to be more consistent with the convention
+    used for Latvian Summer Time (1918-9) and for British Summer Time.
+
   Changes to build procedure
 
     The default installation procedure no longer creates the
@@ -35,6 +39,11 @@ Unreleased, experimental changes
     zic has been ported to GCC 8's -Wstringop-truncation option.
     (Problem reported by Martin Sebor.)
 
+  Changes to documentation and commentary
+
+    The theory.html file now mentions the POSIX limit of six chars
+    per abbreviation, and lists alphabetic abbreviations used.
+
 
 Release 2017c - 2017-10-20 14:49:34 -0700
 

asia

@@ -2066,8 +2066,8 @@ Zone Asia/Kuching	7:21:20	-	LMT	1926 Mar
 
 # Maldives
 # Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
-Zone	Indian/Maldives	4:54:00 -	LMT	1880 # Male
-			4:54:00	-	MMT	1960 # Male Mean Time
+Zone	Indian/Maldives	4:54:00 -	LMT	1880 # Malé
+			4:54:00	-	MMT	1960 # Malé Mean Time
 			5:00	-	+05
 
 # Mongolia

southamerica

@@ -579,7 +579,7 @@ Link America/Curacao America/Aruba
 # Zone	NAME		GMTOFF	RULES	FORMAT	[UNTIL]
 Zone	America/La_Paz	-4:32:36 -	LMT	1890
 			-4:32:36 -	CMT	1931 Oct 15 # Calamarca MT
-			-4:32:36 1:00	BOST	1932 Mar 21 # Bolivia ST
+			-4:32:36 1:00	BST	1932 Mar 21 # Bolivia ST
 			-4:00	-	-04
 
 # Brazil

theory.html

@@ -240,7 +240,7 @@ <h2 id="naming">Names of time zone rules</h2>
 zone rules.  It is intended to be an exhaustive list of names for
 geographic regions as described above; this is a subset of the names
 in the data.  Although a '<code>zone1970.tab</code>' location's longitude
-corresponds to its LMT offset with one hour for every 15 degrees east
+corresponds to its LMT offset with one hour for every 15&deg; east
 longitude, this relationship is not exact.
 </p>
 
@@ -279,7 +279,7 @@ <h2 id="abbreviations">Time zone abbreviations</h2>
 in decreasing order of importance:
 <ul>
   <li>
-	Use three or more characters that are ASCII alphanumerics or
+	Use three to six characters that are ASCII alphanumerics or
 		'<code>+</code>' or '<code>-</code>'.
 		Previous editions of this database also used characters like
 		'<code> </code>' and '<code>?</code>', but these
@@ -308,12 +308,93 @@ <h2 id="abbreviations">Time zone abbreviations</h2>
 		We assume that applications translate them to other languages
 		as part of the normal localization process; for example,
 		a French application might translate 'EST' to 'HNE'.
+
+<p><small>These abbreviations (for standard/daylight/etc. time) are:
+ACST/ACDT Australian Central,
+AST/ADT/APT/AWT/ADDT Atlantic,
+AEST/AEDT Australian Eastern,
+AHST/AHDT Alaska-Hawaii,
+AKST/AKDT Alaska,
+AWST/AWDT Australian Western,
+BST/BDT Bering,
+CAT/CAST Central Africa,
+CET/CEST/CEMT Central European,
+ChST Chamorro,
+CST/CDT/CWT/CPT/CDDT Central [North America],
+CST/CDT China,
+GMT/BST/BDST Greenwich,
+EAT East Africa,
+EST/EDT/EWT/EPT/EDDT Eastern [North America],
+EET/EEST Eastern European,
+GST Guam,
+HST/HDT Hawaii,
+HKT/HKST Hong Kong,
+IST India,
+IST/IDT/IDDT Israel,
+JST/JDT Japan,
+KST/KDT Korea,
+MET/MEST Middle European (a backward-compatibility alias for Central European),
+MSK/MSD Moscow,
+MST/MDT/MWT/MPT/MDDT Mountain,
+NST/NDT/NWT/NPT/NDDT Newfoundland,
+NZMT/NZST New Zealand through 1945,
+NZST/NZDT New Zealand 1946&ndash;present,
+PKT/PKST Pakistan,
+PST/PDT/PWT/PPT/PDDT Pacific,
+SAST South Africa,
+SST Samoa,
+WAT/WAST West Africa,
+WET/WEST/WEMT Western European,
+WIB Waktu Indonesia Barat,
+WIT Waktu Indonesia Timur,
+WITA Waktu Indonesia Tengah,
+YST/YDT/YWT/YPT/YDDT Yukon</small>.</p>
   </li>
   <li>
 	For zones whose times are taken from a city's longitude, use the
-		traditional <var>x</var>MT notation, e.g. 'PMT' for
-		Paris Mean Time.
-		The only name like this in current use is 'GMT'.
+traditional <var>x</var>MT notation. The only abbreviation like this
+in current use is 'GMT'. The others are for timestamps before 1960,
+except that Monrovia Mean Time persisted until 1972. Typically,
+numeric abbreviations (e.g., '<code>-</code>004430' for MMT) would
+cause trouble here, as the numeric strings would exceed the POSIX length limit.
+
+<p><small>These abbreviations are:
+AMT Amsterdam, Asunción, Athens;
+BMT Baghdad, Bangkok, Batavia, Bern, Bogotá, Bridgetown, Brussels, Bucharest;
+CMT Calamarca, Caracas, Chisinau, Colón, Copenhagen, Córdoba;
+DMT Dublin;
+EMT Easter;
+FFMT Fort-de-France;
+FMT Funchal;
+GMT Greenwich;
+HMT Havana, Helsinki, Horta, Howrah;
+IMT Irkutsk, Istanbul;
+JMT Jerusalem;
+KMT Kaunas, Kiev, Kingston;
+LMT Lima, Lisbon, local, Luanda;
+MMT Macassar, Madras, Malé, Managua, Minsk, Monrovia, Montevideo, Moratuwa,
+ Moscow;
+PLMT Phù Liễn;
+PMT Paramaribo, Paris, Perm, Pontianak, Prague;
+PMMT Port Moresby;
+QMT Quito;
+RMT Rangoon, Riga, Rome;
+SDMT Santo Domingo;
+SJMT San José;
+SMT Santiago, Simferopol, Singapore, Stanley;
+TBMT Tbilisi;
+TMT Tallinn, Tehran;
+WMT Warsaw</small>.</p>
+
+<p><small>A few abbreviations also follow the pattern that
+GMT/BST/BDST established for time in the UK. They are:
+
+CMT/BST for Calamarca Mean Time and Bolivian Summer Time
+1890&ndash;1932, MMT/MST/MDST for Moscow 1880&ndash;1919, and RMT/LST
+for Riga Mean Time and Latvian Summer time 1880&ndash;1926.
+An extra-special case is SET for Swedish Time (<em>svensk
+normaltid</em>) 1879&ndash;1899, 3&deg; west of the Stockholm
+Observatory.</small></p>
   </li>
   <li>
 	Use 'LMT' for local mean time of locations before the introduction
@@ -340,32 +421,6 @@ <h2 id="abbreviations">Time zone abbreviations</h2>
 		history tends to use numeric abbreviations and a particular
 		entry could go either way, use a numeric abbreviation.
   </li>
-</ul>
-    [The remaining guidelines predate the introduction of <code>%z</code>.
-    They are problematic as they mean tz data entries invent
-    notation rather than record it.  These guidelines are now
-    deprecated and the plan is to gradually move to <code>%z</code> for
-    inhabited locations and to "<code>-</code>00" for uninhabited locations.]
-<ul>
-  <li>
-	If there is no common English abbreviation, abbreviate the English
-		translation of the usual phrase used by native speakers.
-		If this is not available or is a phrase mentioning the country
-		(e.g. "Cape Verde Time"), then:
-	<ul>
-	  <li>
-		When a country is identified with a single or principal zone,
-			append 'T' to the country's ISO	code, e.g. 'CVT' for
-			Cape Verde Time.  For summer time append 'ST';
-			for double summer time append 'DST'; etc.
-	  </li>
-	  <li>
-		Otherwise, take the first three letters of an English place
-			name identifying each zone and append 'T', 'ST', etc.
-			as before; e.g. 'CHAST' for CHAtham Summer Time.
-	  </li>
-	</ul>
-  </li>
   <li>
 	Use UT (with time zone abbreviation '<code>-</code>00') for
 		locations while uninhabited.  The leading

tz-link.htm

@@ -865,7 +865,7 @@ <h2 id="notation">Time notation</h2>
 the international standard date and time notation</a> is a good
 summary of
 <a
-href="https://www.iso.org/standard/40874.html"><abbr><em>ISO</abbr>
+href="https://www.iso.org/standard/40874.html"><em><abbr>ISO</abbr>
 8601:2004 &ndash; Data elements and interchange formats &ndash; Information
 interchange &ndash; Representation of dates and times</em></a>.</li>
 <li>
@@ -897,7 +897,7 @@ <h2 id="notation">Time notation</h2>
 "<abbr>CST</abbr>". The <code><abbr>tz</abbr></code>
 database contains English abbreviations for many time stamps;
 unfortunately some of these abbreviations were merely the database maintainers'
-inventions, and are gradually being removed.</li>
+inventions, and these have been removed when possible.</li>
 <li>Numeric time zone abbreviations typically count hours east of
 <abbr>UT</abbr>, e.g., +09 for Japan and
 &minus;10 for Hawaii. However, the <abbr>POSIX</abbr>