Actually the below paragraph made me confused: from the link :
http://ruby.about.com/od/control/a/The-Case-Statement.htm

What Type?
==============

A common use for the case statement is to determine the type of the 
value and do something different depending on its type. Though this 
breaks Ruby's customary duck typing, it's sometimes necessary to get 
things done. This works by using the Class#=== (technically, the 
Module#===) operator, which tests if the right-hand side is_a? left-hand 
side. The syntax is simple and elegant.

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