The "embedded actions" plugin 
=============================
BASIC USAGE
  Just like the traditional render :partial, embedded actions allow you to
  refactor your views and extract presentation logic and templates into separate
  files.
  Unlike partials, embedded actions also let you define business logic to be
  performed before the partial is included. That logic is encapsulated in the
  already well understood metaphor of an action inside a controller.
  So a simple call like
  <%= embed_action :controller => "songs", :action => "top10" %>
  lets you include an html fragment containing the top 10 songs into any of your
  pages, regardless of which controller, action or view wants to do the including.
CACHING
  Embedded actions can provide caching of their results (allowing for different 
  parameters) just like page caching, but at the level of html fragments. 
  So your dynamic pages can still be rendered dynamically, but some of the embedded
  actions can be cached (and expired) independently.
  Just declare an action as 'cacheable' in a way similar to page caching, 
  by invoking "caches_embedded" with the name of the action to cache.
  class TestController < ApplicationController
    caches_embedded :user_list
    def user_list
      ...
    end
  end
  Cached fragments can be invalidated with calls to expires_embedded, but you must
  remember to use the same set of parameters used to embed the cached action in
  the first place.
  Additionally, the underlying fragment caching mechanism can be passed 
  an options hash in the following manner:
    caches_embedded :user_list, :ttl => 60.minutes
RESPONDS_TO
  Actions can use Rails' responds_to to provide different behaviours when invoked 
  normally or embedded in another view.
  
  class TestController < ApplicationController
    def user_list
      responds_to do |format|
        format.html     {render :layout => :application}
        format.embedded {render :layout => false}
      end
    end
  end
SOURCE CODE
  The official repository for embedded_actions is in GitHub:
  
  https://github.com/sd/embedded-actions/tree/master
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Copyright (c) 2007, 2008 Sebastian Delmont <sd@notso.net> 
Copyright (c) 2007, 2008 StreetEasy / NMD Interactive <https://www.streeteasy.com/> 
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are permitted provided that the following conditions are met:
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CONTRIBUTORS
- Sebastian Delmont <sd@notso.net>
- Jerret Taylor <jerrett@gmail.com>
- Ryan Barber <rfb@skyscraper.nu>
- Andreas Simon <asimon@med4you.de>
- Jonathan Boler <galatians@gmail.com>
RELEASE HISTORY
1.0 - Oct 23 2007
  First widespread release.
1.0.1 - Oct 30 2007 
  Fixed bug that was causing a "Content-encoding: identity" to leak 
  to all requests.
1.0.2 - Nov 29 2007
  Fixed bug (thanks Jerret) that caused caching settings to leak 
  to actions with the same name in other controllers.
1.1 - Dec 4 2007
  Passthrough options for fragment caching (Ryan).
  Support for namespaced controllers in caching (Jerret). 
  Minor bug fixes.
1.1.1 - Feb 20 2008
  Allow symbol names for controllers and actions (Andreas)
  Fixed deprecated 'require_gem' in test environment (Andreas)
1.1.2 - Dec 5 2008
  Simplified responds_to behaviour
  Rails 2.2 compatibility (Jonathan)