# File lib/action_controller/base.rb, line 1216
      def expires_in(seconds, options = {}) #:doc:
        cache_control = response.headers["Cache-Control"].split(",").map {|k| k.strip }

        cache_control << "max-age=#{seconds}"
        cache_control.delete("no-cache")
        if options[:public]
          cache_control.delete("private")
          cache_control << "public"
        else
          cache_control << "private"
        end
        
        # This allows for additional headers to be passed through like 'max-stale' => 5.hours
        cache_control += options.symbolize_keys.reject{|k,v| k == :public || k == :private }.map{ |k,v| v == true ? k.to_s : "#{k.to_s}=#{v.to_s}"}
        
        response.headers["Cache-Control"] = cache_control.join(', ')
      end