diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
new file mode 100644
index 4b35169..615b2b0
*** a/doc/src/sgml/config.sgml
--- b/doc/src/sgml/config.sgml
*************** local0.*    /var/log/postgresql
*** 3086,3091 ****
--- 3086,3095 ----
          any time-zone-dependent <literal>%</literal>-escapes, the computation
          is done in the zone specified
          by <xref linkend="guc-log-timezone">.)
+         The supported <literal>%</literal>-escapes are similar to those
+         listed in the Open Group's <ulink
+         url="http://pubs.opengroup.org/onlinepubs/009695399/functions/strftime.html">strftime
+         </ulink> specification.
          Note that the system's <systemitem>strftime</systemitem> is not used
          directly, so platform-specific (nonstandard) extensions do not work.
         </para>