Docs update

[SVN r13144]

doc/reference/if_then.htm

@@ -29,6 +29,8 @@
 <h2><a name="BOOST_PP_IF_THEN">#define BOOST_PP_IF_THEN</a>(C,T)</h2>
  <p>Expands to <code>T</code> if <code>C != 0</code> and to nothing if <code>C == 0</code>.</p>
 
+<p>For example, <code><a href="if_then.htm#BOOST_PP_IF_THEN">BOOST_PP_IF_THEN</a>(1,^)</code> expands to <code>^</code>.</p>
+
 <hr>
 
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