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app/helpers/application_helper.rb

@@ -24,6 +24,7 @@ module ApplicationHelper
       :target => "_blank"
   end 
 
+  # Produces a cache key for uniquely identifying cached fragments.
   def cache_key_for(klass, identifier="all")
     count          = klass.count
     max_updated_at = klass.maximum(:updated_at).try(:utc).try(:to_s, :number)