diff --git a/actionpack/lib/action_controller/metal.rb b/actionpack/lib/action_controller/metal.rb
index e5db31061b..585bd5e5ab 100644
--- a/actionpack/lib/action_controller/metal.rb
+++ b/actionpack/lib/action_controller/metal.rb
@@ -201,19 +201,23 @@ def to_a #:nodoc:
     class_attribute :middleware_stack
     self.middleware_stack = ActionController::MiddlewareStack.new
 
-    def self.inherited(base)
+    def self.inherited(base) #nodoc:
       base.middleware_stack = self.middleware_stack.dup
       super
     end
 
+    # Adds given middleware class and its args to bottom of middleware_stack
     def self.use(*args, &block)
       middleware_stack.use(*args, &block)
     end
 
+    # Alias for middleware_stack
     def self.middleware
       middleware_stack
     end
 
+    # Makes the controller a rack endpoint that points to the action in
+    # the given env's action_dispatch.request.path_parameters key.
     def self.call(env)
       action(env['action_dispatch.request.path_parameters'][:action]).call(env)
     end