Add a little to index operator class discussion.

diff --git a/doc/src/sgml/indices.sgml b/doc/src/sgml/indices.sgml
index 8dc410f263a793389c044e2683b9f530650f051e..32aa5e7892ebcc82e30eb598a582a3ce03d53b66 100644 (file)
--- a/doc/src/sgml/indices.sgml
+++ b/doc/src/sgml/indices.sgml
@@ -110,9 +110,11 @@
    integers.  In practice the default operator class for the field's
    datatype is usually sufficient.  The main point of having operator classes
    is that for some datatypes, there could be more than one meaningful
-   ordering.  For an index on such a datatype, we could select which
-   ordering we wanted by selecting the proper operator class.  There
-   are also some operator classes with special purposes:
+   ordering.  For example, we might want to sort a complex-number datatype
+   either by absolute value or by real part.  We could do this by defining
+   two operator classes for the datatype and then selecting the proper
+   class when making an index.  There are also some operator classes with
+   special purposes:
 
    <itemizedlist>
     <listitem>