rails源代码里reloadable是如何用途的？

在actioncontroller的base.rb中，class Base有如下定义：
include Reloadable::Subclasses
其中Reloadable定义如下：

module Reloadable
  class << self
    def included(base) #nodoc:
      raise TypeError, "Only Classes can be Reloadable!" unless base.is_a? Class
      
      unless base.respond_to?(:reloadable?)
        class << base
          define_method(:reloadable?) { true }
        end
      end
    end
    
    def reloadable_classes
      included_in_classes.select { |klass| klass.reloadable? }
    end
  end
  
  # Captures the common pattern where a base class should not be reloaded,
  # but its subclasses should be.
  module Subclasses
    def self.included(base) #nodoc:
      base.send :include, Reloadable
      (class << base; self; end).send(:define_method, :reloadable?) do
         base != self
      end
    end
  end
end

这里不是很懂include Reloadable::Subclasses的意思，为什么需要在Reloadable内部还需要定义一个Subclasses呢？