class Symbol: A +Symbol+ object represents a named identifier inside the Ruby interpreter. literals.| docs.ruby-lang.org
class String: A +String+ object has an arbitrary sequence of bytes, typically representing text or binary data. new or as literals.| docs.ruby-lang.org
class Regexp: en. wikipedia.| docs.ruby-lang.org
class Object: Object is the default root of all Ruby objects. Object inherits from BasicObject which allows creating alternate object hierarchies.| docs.ruby-lang.org
class Hash: A +Hash+ maps each of its unique keys to a specific value. An Array index is always an Integer.| docs.ruby-lang.org
module Kernel: The Kernel module is included by class Object, so its methods are available in every Ruby object. The Kernel instance methods are documented in class| docs.ruby-lang.org