object_model.rb

module Printable
  def print
  end

  def prepare_cover
  end
end

module Document
  def print_to_screen
    prepare_cover
    format_for_screen
    print
  end

  def format_for_screen
  end

  def print
  end
end

class Book
  include Document
  include Printable
end

p  Book.ancestors # => [Book, Printable, Document, Object, Kernel, BasicObject]