1 files changed, 8 insertions, 2 deletions
diff --git a/actionpack/lib/action_controller/metal/renderers.rb b/actionpack/lib/action_controller/metal/renderers.rb
index 5272dc6cdb..0443b73953 100644
--- a/actionpack/lib/action_controller/metal/renderers.rb
+++ b/actionpack/lib/action_controller/metal/renderers.rb
@@ -6,6 +6,12 @@ module ActionController
     Renderers.add(key, &block)
   end
 
+  class MissingRenderer < LoadError
+    def initialize(format)
+      super "No renderer defined for format: #{format}"
+    end
+  end
+
   module Renderers
     extend ActiveSupport::Concern
 
@@ -36,8 +42,8 @@ module ActionController
       nil
     end
 
-    # Hash of available renderers, mapping a renderer name to its proc.
-    # Default keys are :json, :js, :xml.
+    # A Set containing renderer names that correspond to available renderer procs.
+    # Default values are <tt>:json</tt>, <tt>:js</tt>, <tt>:xml</tt>.
     RENDERERS = Set.new
 
     # Adds a new renderer to call within controller actions.