Extended intro to Authentication part to include pointers to tech overview and namespace config

src/docbkx/springsecurity.xml

@@ -135,11 +135,26 @@
     <title>Authentication</title>
 
     <partintro>
-      <para>In this part of the reference guide we will examine individual
+      <para>We've already introduced Spring Security's authentication architecture
+        in the <link xlink:href="#technical-overview">Technical Overview</link> chapter.
+        In this part of the reference guide we will examine individual
       authentication mechanisms and their corresponding
       <literal>AuthenticationProvider</literal>s. We'll also look at how to
       configure authentication more generally, including if you have several
       authentication approaches that need to be chained together.</para>
+      <para>
+        With some exceptions, we will be discussing the full details of Spring Security
+        bean configuration rather than the shorthand
+        <link xlink:href="#namespace-config">namespace syntax</link>. You should review
+        the introduction to using namespace configuration and the options it provides
+        to see if they will meet your needs. As you come to use the framework more,
+        and need to customize the internal behaviour, you will probably want to understand
+        more about how the individual services are implemented, which classes to look at
+        extending and so on. This part is more targeted at providing this kind of information.
+        We'd recommend that you supplement the content by browsing the Javadoc and the source
+        itself <footnote><para>Links to both Javadoc APIs and browsable source cross-reference
+        are available from the project web site.</para></footnote>.
+      </para>
     </partintro>
 
     <xi:include href="common-auth-services.xml" />