Re: Second-granular timezone offset format not documented

PG Doc comments form <noreply@postgresql.org> writes:
> Here is an example of a format that I don't think the documentation
> currently covers:
> janus=> set timezone to 'America/Mexico_City';
> SET
> janus=> select '1920-12-25' :: timestamptz;
>          timestamptz          
> ------------------------------
>  1920-12-25 00:00:00-06:36:36
> (1 row)

Yeah, fair point.  There's a passing mention of fractional-minute
offsets in Appendix B, but the main docs don't cover it at all.
I propose the attached draft patch.

            regards, tom lane

diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
index c473d6a746..bd3bf5768c 100644
--- a/doc/src/sgml/datatype.sgml
+++ b/doc/src/sgml/datatype.sgml
@@ -2020,19 +2020,27 @@ MINUTE TO SECOND
          </row>
          <row>
           <entry><literal>04:05:06.789-8</literal></entry>
-          <entry>ISO 8601</entry>
+          <entry>ISO 8601, with time zone as UTC offset</entry>
          </row>
          <row>
           <entry><literal>04:05:06-08:00</literal></entry>
-          <entry>ISO 8601</entry>
+          <entry>ISO 8601, with time zone as UTC offset</entry>
          </row>
          <row>
           <entry><literal>04:05-08:00</literal></entry>
-          <entry>ISO 8601</entry>
+          <entry>ISO 8601, with time zone as UTC offset</entry>
          </row>
          <row>
           <entry><literal>040506-08</literal></entry>
-          <entry>ISO 8601</entry>
+          <entry>ISO 8601, with time zone as UTC offset</entry>
+         </row>
+         <row>
+          <entry><literal>040506+0730</literal></entry>
+          <entry>ISO 8601, with fractional-hour time zone as UTC offset</entry>
+         </row>
+         <row>
+          <entry><literal>040506+07:30:00</literal></entry>
+          <entry>UTC offset specified to seconds (not allowed in ISO 8601)</entry>
          </row>
          <row>
           <entry><literal>04:05:06 PST</literal></entry>
@@ -2068,17 +2076,21 @@ MINUTE TO SECOND
           <entry><literal>PST8PDT</literal></entry>
           <entry>POSIX-style time zone specification</entry>
          </row>
+         <row>
+          <entry><literal>-8:00:00</literal></entry>
+          <entry>UTC offset for PST</entry>
+         </row>
          <row>
           <entry><literal>-8:00</literal></entry>
-          <entry>ISO-8601 offset for PST</entry>
+          <entry>UTC offset for PST (ISO 8601 extended format)</entry>
          </row>
          <row>
           <entry><literal>-800</literal></entry>
-          <entry>ISO-8601 offset for PST</entry>
+          <entry>UTC offset for PST (ISO 8601 basic format)</entry>
          </row>
          <row>
           <entry><literal>-8</literal></entry>
-          <entry>ISO-8601 offset for PST</entry>
+          <entry>UTC offset for PST (ISO 8601 basic format)</entry>
          </row>
          <row>
           <entry><literal>zulu</literal></entry>
@@ -2086,7 +2098,7 @@ MINUTE TO SECOND
          </row>
          <row>
           <entry><literal>z</literal></entry>
-          <entry>Short form of <literal>zulu</literal></entry>
+          <entry>Short form of <literal>zulu</literal> (also in ISO 8601)</entry>
          </row>
         </tbody>
        </tgroup>
@@ -2395,6 +2407,24 @@ TIMESTAMP WITH TIME ZONE '2004-10-19 10:23:54+02'
      </para>
     </note>

+    <para>
+     In the <acronym>ISO</acronym> style, the time zone is always shown as
+     a signed numeric offset from UTC, with positive sign used for zones
+     east of Greenwich.  The offset will be shown
+     as <replaceable>hh</replaceable> (hours only) if it is an integral
+     number of hours, else
+     as <replaceable>hh</replaceable>:<replaceable>mm</replaceable> if it
+     is an integral number of minutes, else
+     <replaceable>hh</replaceable>:<replaceable>mm</replaceable>:<replaceable>ss</replaceable>.
+     (The last case is not possible with any modern time zone standard,
+     but it can appear when working with timestamps that predate the
+     introduction of standardized time zones.)
+     In the other date styles, the time zone is shown as an alphabetic
+     abbreviation if one is in common use in the current zone; otherwise
+     it appears as a signed numeric offset in ISO 8601 basic format
+     (<replaceable>hh</replaceable> or <replaceable>hhmm</replaceable>).
+    </para>
+
     <para>
      In the <acronym>SQL</acronym> and POSTGRES styles, day appears before
      month if DMY field ordering has been specified, otherwise month appears