ActiveModel 내의 include/extend 관계

module ActiveModel
  extend ActiveSupport::Autoload

  autoload :AttributeMethods
  autoload :BlockValidator, 'active_model/validator'
  autoload :Callbacks
  autoload :Conversion
  autoload :Dirty
  autoload :EachValidator, 'active_model/validator'
  autoload :ForbiddenAttributesProtection
  autoload :Lint
  autoload :Model
  autoload :Name, 'active_model/naming'
  autoload :Naming
  autoload :SecurePassword
  autoload :Serialization
  autoload :TestCase
  autoload :Translation
  autoload :Validations
  autoload :Validator
...