Clarified highly-misleading (unset) casting example. Resolves bug #55164.

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@322117 c90b9560-bf6c-de11-be94-00142212c4b1

reference/var/functions/unset.xml

@@ -228,16 +228,30 @@ unset($foo1, $foo2, $foo3);
     </programlisting>
    </example>
    <example>
-    <title>Using (unset) casting</title>
+    <title>Using <literal>(unset)</literal> casting</title>
+    <para>
+     <literal>(unset)</literal> casting is often confused with the
+     <function>unset</function> function. <literal>(unset)</literal>
+     casting serves only as a <literal>NULL</literal>-type cast, for
+     completeness. It does not alter the variable it's casting.
+    </para>
     <programlisting role="php">
 <![CDATA[
 <?php
 $name = 'Felipe';
 
 var_dump((unset) $name);
+var_dump($name);
 ?>
 ]]>
     </programlisting>
+    &example.outputs;
+    <screen>
+<![CDATA[
+NULL
+string(6) "Felipe"
+]]>
+    </screen>
    </example>
   </para>
  </refsect1>