Edited the Moose section.

sections/advanced_oo.pod

@@ -74,6 +74,8 @@ or more specific about what they produce.
 
 =head3 Immutability
 
+Z<immutability>
+
 A common pattern among programmers new to object orientation is to treat
 objects as if they were bundles of records which use methods to get and set
 internal values.  While this is simple to implement and easy to understand, it

sections/chapter_07.pod

@@ -1,5 +1,19 @@
 =head1 Objects
 
+Writing large programs requires more discipline than writing small programs,
+due to the difficulty of managing all of the details of your program
+simultaneously.  Abstraction (finding and exploiting similarities and
+near-similarities) and encapsulation (grouping specific details together and
+accessing them where they belong) are essential to managing this complexity.
+
+Functions help, but functions by themselves aren't sufficient for the largest
+programs.  Object orientation is a popular technique for grouping functions
+together into classes of related behaviors.
+
+Perl 5's default object system is minimal.  It's very flexible--you can build
+almost any other object system you want on top of it--but it provides little
+assistance for performing the most common tasks simply and easily.
+
 L<moose>
 
 L<blessed_references>