[Rails] @content_for_sidebar?

[Dean]

Okay, I see this instance variable places, but I can not determine if it is real 
or where the content comes from.  I've tried views/<controller>/sidebar.rhtml, 
_sidebar.rhtml, views/layouts/sidebar.rhtml and views/layouts/_sidebar.rhtml.

Does this actually exist?  What's the Rails Way to make a good sidebar?

http://www.google.com/search?q=content_for_sidebar

Thanks,
--Dean
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