1 files changed, 35 insertions, 0 deletions
diff --git a/activesupport/lib/active_support/concern.rb b/activesupport/lib/active_support/concern.rb
index eb31f7cad4..408d327dd7 100644
--- a/activesupport/lib/active_support/concern.rb
+++ b/activesupport/lib/active_support/concern.rb
@@ -1,3 +1,38 @@
+# A typical module looks like this
+#
+#   module M
+#     def self.included(base)
+#       base.send(:extend, ClassMethods)
+#       base.send(:include, InstanceMethods)
+#       scope :foo, :conditions => {:created_at => nil}
+#     end
+#
+#     module ClassMethods
+#       def cm; puts 'I am class method'; end
+#     end
+#
+#     module InstanceMethods
+#       def im; puts 'I am instance method'; end
+#     end
+#   end
+#
+# By using <tt>ActiveSupport::Concern</tt> above module could be written as:
+#
+#   module M
+#     extend ActiveSupport::Concern
+#
+#    included do 
+#       scope :foo, :conditions => {:created_at => nil}
+#     end
+#
+#     module ClassMethods
+#       def cm; puts 'I am class method'; end
+#     end
+#
+#     module InstanceMethods
+#       def im; puts 'I am instance method'; end
+#     end
+#   end
 module ActiveSupport
   module Concern
     def self.extended(base)