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+src/timezone/tznames/README
+
+tznames
+=======
+
+This directory contains files with timezone sets for PostgreSQL.  The problem
+is that time zone abbreviations are not unique throughout the world and you
+might find out that a time zone abbreviation in the `Default' set collides
+with the one you wanted to use.  This can be fixed by selecting a timezone
+set that defines the abbreviation the way you want it.  There might already
+be a file here that serves your needs.  If not, you can create your own.
+
+In order to use one of these files, you need to set
+
+   timezone_abbreviations = 'xyz'
+
+in any of the usual ways for setting a parameter, where xyz is the filename
+that contains the desired time zone abbreviations.
+
+If you do not find an appropriate set of abbreviations for your geographic
+location supplied here, please report this to <pgsql-hackers@lists.postgresql.org>.
+Your set of time zone abbreviations can then be included in future releases.
+For the time being you can always add your own set.
+
+Typically a custom abbreviation set is made by including the `Default' set
+and then adding or overriding abbreviations as necessary.  For examples,
+see the `Australia' and `India' files.
+
+The files named Africa.txt, etc, are not intended to be used directly as
+time zone abbreviation files. They contain reference definitions of time zone
+abbreviations that can be copied into a custom abbreviation file as needed.
+These files contain most of the time zone abbreviations that were shown
+in the IANA timezone database circa 2010.
+
+However, it turns out that many of these abbreviations had simply been
+invented by the IANA timezone group, and do not have currency in real-world
+use.  The IANA group have changed their policy about that, and now prefer to
+use numeric UTC offsets whenever there's not an abbreviation with known
+real-world popularity.  A lot of these abbreviations therefore no longer
+appear in the IANA data, and so are marked "obsolete" in these data files.