What test Ruby perform on the `when` clause statement before calling `.===` operator?

What test Ruby perform on the `when` clause statement before calling
`.===` operator?

References

Reference NO 1

http://stackoverflow.com/questions/15190674/what-test-ruby-perform-on-the-when-clause-statement-before-calling-oper

Reference NO 2

http://stackoverflow.com/questions/2259775/what-do-you-call-the-operator-in-ruby

Reference NO 3

https://www.ruby-forum.com/topic/4411568

Reference NO 4

http://ruby.about.com/od/control/a/The-Case-Statement.htm

Reference NO 5

http://www.tutorialspoint.com/ruby/ruby_operators.htm

Reference NO 6

http://www.ruby-doc.org/docs/ProgrammingRuby/html/tut_expressions.html

Reference NO 7

http://www.rubyinside.com/21-ruby-tricks-902.html

Reference NO 8

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