Ruby x.kind_of?

module M; end

class A; end

class B < A
  include M
end

b = B.new

b.kind_of? A # => true
b.kind_of? B # => true
b.kind_of? M # => true

b.class == A # => true
b.class == B # => false
b.class == M # => false

A === b # => true
B === b # => true
M === b # => true

Reference:
http://refactormycode.com/codes/487-x-kind_of-myclass-or-x-class-myclass