Documentation: Added small comments to Observering module

activemodel/lib/active_model/observing.rb

@@ -48,6 +48,7 @@ module ActiveModel
         observers.each { |o| instantiate_observer(o) }
       end
 
+      # Add a new Observer to the pool
       def add_observer(observer)
         unless observer.respond_to? :update
           raise ArgumentError, "observer needs to respond to `update'"
@@ -55,12 +56,14 @@ module ActiveModel
         observer_instances << observer
       end
 
+      # Notify list of observers of a change
       def notify_observers(*arg)
         for observer in observer_instances
           observer.update(*arg)
         end
       end
 
+      # Total number of observers
       def count_observers
         observer_instances.size
       end