diff --git a/doc/src/sgml/datatype.sgml b/doc/src/sgml/datatype.sgml
index 66510ee031..1c568e5022 100644
--- a/doc/src/sgml/datatype.sgml
+++ b/doc/src/sgml/datatype.sgml
@@ -2869,10 +2869,46 @@ P <optional> <replaceable>years</replaceable>-<replaceable>months</replaceable>-
     </para>
 
     <para>
-     Field values can have fractional parts:  for example, <literal>'1.5
+     Internally <type>interval</type> values are stored as three integral
+     fields: months, days, and microseconds.  These fields are kept
+     separate because the number of days in a month varies, while a day
+     can have 23 or 25 hours if a daylight savings time transition is
+     involved.  An interval input string that uses other units is
+     normalized into this format, and then reconstructed in a standardized
+     way for output, for example:
+
+<programlisting>
+SELECT '2 years 15 months 100 weeks 99 hours 123456789 milliseconds'::interval;
+               interval
+---------------------------------------
+ 3 years 3 mons 700 days 133:17:36.789
+</programlisting>
+
+     Here weeks, which are understood as <quote>7 days</quote>, have been
+     kept separate, while the smaller and larger time units were
+     combined and normalized.  It is possible to use the
+     functions <function>justify_days</function>
+     and <function>justify_hours</function> to convert large days or
+     hours values into the next higher field:
+
+<programlisting>
+SELECT justify_days('2 years 15 months 100 weeks 99 hours 123456789 milliseconds'::interval);
+             justify_days
+--------------------------------------
+ 5 years 2 mons 10 days 133:17:36.789
+
+SELECT justify_hours('2 years 15 months 100 weeks 99 hours 123456789 milliseconds'::interval);
+            justify_hours
+--------------------------------------
+ 3 years 3 mons 705 days 13:17:36.789
+</programlisting>
+    </para>
+
+    <para>
+     Input field values can have fractional parts, for example <literal>'1.5
      weeks'</literal> or <literal>'01:02:03.45'</literal>.  However,
-     because interval internally stores only three integer units (months,
-     days, microseconds), fractional units must be spilled to smaller
+     because interval internally stores only integer fields,
+     fractional units must be spilled to smaller
      units.  Fractional parts of units greater than months are rounded to
      be an integer number of months, e.g. <literal>'1.5 years'</literal>
      becomes <literal>'1 year 6 mons'</literal>.  Fractional parts of
@@ -2922,33 +2958,6 @@ P <optional> <replaceable>years</replaceable>-<replaceable>months</replaceable>-
       </tgroup>
      </table>
 
-    <para>
-     Internally <type>interval</type> values are stored as months, days,
-     and microseconds. This is done because the number of days in a month
-     varies, and a day can have 23 or 25 hours if a daylight savings
-     time adjustment is involved.  The months and days fields are integers
-     while the microseconds field can store fractional seconds.  Because intervals are
-     usually created from constant strings or <type>timestamp</type> subtraction,
-     this storage method works well in most cases, but can cause unexpected
-     results:
-
-<programlisting>
-SELECT EXTRACT(hours from '80 minutes'::interval);
- date_part
------------
-         1
-
-SELECT EXTRACT(days from '80 hours'::interval);
- date_part
------------
-         0
-</programlisting>
-
-     Functions <function>justify_days</function> and
-     <function>justify_hours</function> are available for adjusting days
-     and hours that overflow their normal ranges.
-    </para>
-
    </sect2>
 
    <sect2 id="datatype-interval-output">
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index cf3de80394..480a8dcb60 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -10461,6 +10461,20 @@ SELECT EXTRACT(YEAR FROM TIMESTAMP '2001-02-16 20:38:40');
     </variablelist>
    </para>
 
+   <para>
+    When processing <type>interval</type> input,
+    the <function>extract</function> function produces field values that
+    match the interpretation used by the interval output function.  This
+    can produce surprising results if one starts with a non-normalized
+    interval representation, for example:
+<screen>
+SELECT INTERVAL '80 minutes';
+<lineannotation>Result: </lineannotation><computeroutput>01:20:00</computeroutput>
+SELECT EXTRACT(MINUTES FROM INTERVAL '80 minutes');
+<lineannotation>Result: </lineannotation><computeroutput>20</computeroutput>
+</screen>
+   </para>
+
    <note>
     <para>
      When the input value is +/-Infinity, <function>extract</function> returns