Clarify that multiple authentication-provider elements can be used in combination.

docs/manual/src/docbook/namespace-config.xml

@@ -329,8 +329,10 @@
   ]]>
         </programlisting> where <literal>myAuthenticationProvider</literal> is the name of a
         bean in your application context which implements
-          <interfacename>AuthenticationProvider</interfacename>. See <xref linkend="ns-auth-manager"
-        /> for more on information on how the Spring Security
+          <interfacename>AuthenticationProvider</interfacename>. You can use multiple
+          <literal>authentication-provider</literal> elements, in which case they will be checked
+        in the order they are declared when attempting to authenticated a user. See <xref
+          linkend="ns-auth-manager"/> for more on information on how the Spring Security
           <interfacename>AuthenticationManager</interfacename> is configured using the namespace. </para>
       <section xml:id="ns-password-encoder">
         <title>Adding a Password Encoder</title>