Per P0 reqs add launch pts + make download obvious. Also misc cpy edits.

native_client_sdk/src/doc/devguide/coding/message-system.rst

 .. _message-system:
 
 ################
 Messaging System
 ################
 
 .. contents::
   :local:
   :backlinks: none
   :depth: 2
 
-This chapter describes the messaging system used to communicate between the
+This section describes the messaging system used to communicate between the
 JavaScript code and the Native Client module's C or C++ code in a
 Native Client application. It introduces the concept of asynchronous
 programming and the basic steps required to set up a Native Client module
-that sends messages to and receive messages from JavaScript. This chapter
+that sends messages to and receive messages from JavaScript. This section
 assumes you are familiar with the material presented in the
-:doc:`Application Structure <application-structure>` chapter.
+:doc:`Application Structure <application-structure>` section.
 
 .. Note::
   :class: note
 
   The "Hello, World" example for getting started with NaCl is used here to
   illustrate basic programming techniques. You can find this code in
   the ``/getting_started/part2`` directory in the Native Client SDK download.
 
 Reference information
 =====================
@@ skipping 375 matching lines @@
   virtual void HandleMessage(const pp::Var& var) {
     if (var.is_dictionary()) {
       pp::VarDictionary dictionary(var);
       // Use the dictionary
       pp::VarArray keys = dictionary.GetKeys();
       // ...
     } else {
       // ...
     }
   }