diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
new file mode 100644
index c7d84b5..efac9eb
*** a/doc/src/sgml/config.sgml
--- b/doc/src/sgml/config.sgml
*************** SET XML OPTION { DOCUMENT | CONTENT };
*** 5366,5371 ****
--- 5366,5372 ----
          partially-significant digits; this is especially useful for dumping
          float data that needs to be restored exactly.  Or it can be set
          negative to suppress unwanted digits.
+         See also <xref linkend="datatype-float">.
         </para>
        </listitem>
       </varlistentry>
diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
new file mode 100644
index f73e6b2..349da60
*** a/doc/src/sgml/datatype.sgml
--- b/doc/src/sgml/datatype.sgml
*************** NUMERIC
*** 681,686 ****
--- 681,696 ----
       from zero will cause an underflow error.
      </para>
  
+     <para>
+      The <xref linkend="guc-extra-float-digits"> setting controls the
+      number of extra significant digits included when a floating point
+      value is converted to text for output.  With the default value of
+      <literal>0</literal>, the output is the same on every platform
+      supported by PostgreSQL, but may not accurately represent the stored
+      value.  Increasing it will produce output that is closer to the stored
+      value, but may be unportable.
+     </para>
+ 
      <indexterm>
       <primary>not a number</primary>
       <secondary>double precision</secondary>