quick edits on the AC::API RDoc [ci skip]

In particular, the fact that ApplicationController is the only
one inheriting from AC::API is not a default. You could say at
most that generators generate them that way, but the creation
of controllers is something which is out of our control because
programmers write controllers by hand.

Instead, we can say that normally, conventionally, as in the
majority of Rails apps, that is the actually the case.

actionpack/lib/action_controller/api.rb

@@ -14,22 +14,22 @@ module ActionController
   # flash, assets, and so on. This makes the entire controller stack thinner,
   # suitable for API applications. It doesn't mean you won't have such
   # features if you need them: they're all available for you to include in
-  # your application, they're just not part of the default API Controller stack.
+  # your application, they're just not part of the default API controller stack.
   #
-  # By default, only the ApplicationController in a \Rails application inherits
-  # from <tt>ActionController::API</tt>. All other controllers in turn inherit
-  # from ApplicationController.
+  # Normally, +ApplicationController+ is the only controller that inherits from
+  # <tt>ActionController::API</tt>. All other controllers in turn inherit from
+  # +ApplicationController+.
   #
   # A sample controller could look like this:
   #
   #   class PostsController < ApplicationController
   #     def index
-  #       @posts = Post.all
-  #       render json: @posts
+  #       posts = Post.all
+  #       render json: posts
   #     end
   #   end
   #
-  # Request, response and parameters objects all work the exact same way as
+  # Request, response, and parameters objects all work the exact same way as
   # <tt>ActionController::Base</tt>.
   #
   # == Renders
@@ -37,18 +37,18 @@ module ActionController
   # The default API Controller stack includes all renderers, which means you
   # can use <tt>render :json</tt> and brothers freely in your controllers. Keep
   # in mind that templates are not going to be rendered, so you need to ensure
-  # your controller is calling either <tt>render</tt> or <tt>redirect</tt> in
-  # all actions, otherwise it will return 204 No Content response.
+  # your controller is calling either <tt>render</tt> or <tt>redirect_to</tt> in
+  # all actions, otherwise it will return 204 No Content.
   #
   #   def show
-  #     @post = Post.find(params[:id])
-  #     render json: @post
+  #     post = Post.find(params[:id])
+  #     render json: post
   #   end
   #
   # == Redirects
   #
   # Redirects are used to move from one action to another. You can use the
-  # <tt>redirect</tt> method in your controllers in the same way as
+  # <tt>redirect_to</tt> method in your controllers in the same way as in
   # <tt>ActionController::Base</tt>. For example:
   #
   #   def create
@@ -56,7 +56,7 @@ module ActionController
   #     # do stuff here
   #   end
   #
-  # == Adding new behavior
+  # == Adding New Behavior
   #
   # In some scenarios you may want to add back some functionality provided by
   # <tt>ActionController::Base</tt> that is not present by default in
@@ -72,18 +72,19 @@ module ActionController
   #
   #   class PostsController < ApplicationController
   #     def index
-  #       @posts = Post.all
+  #       posts = Post.all
   #
   #       respond_to do |format|
-  #         format.json { render json: @posts }
-  #         format.xml  { render xml: @posts }
+  #         format.json { render json: posts }
+  #         format.xml  { render xml: posts }
   #       end
   #     end
   #   end
   #
-  # Quite straightforward. Make sure to check <tt>ActionController::Base</tt>
-  # available modules if you want to include any other functionality that is
-  # not provided by <tt>ActionController::API</tt> out of the box.
+  # Quite straightforward. Make sure to check the modules included in
+  # <tt>ActionController::Base</tt> if you want to use any other
+  # functionality that is not provided by <tt>ActionController::API</tt>
+  # out of the box.
   class API < Metal
     abstract!