How to find out which modules are mixin for a class in Rails?

I'm a new Ruby/Rails guy. Here's one question puzzling me:

Can we find the exact module lists mixin-ed for a class in Rails from the API doc? For example, if we have an instance of one subclass of ActiveRecord::Base, we can use validates method in this class such as following:

class Product < ActiveRecord::Base
  has_many :line_items
  validates :title, :description, :image_url, :presence => true
end

from rails api doc we can find that validates belongs to ActiveModel::Validations::ClassMethods, so ActiveRecore::Base must have ActiveModel::Validations::ClassMethods mixin, but I didn't find anything relating to this in the api reference. Can anyone tell me if I can find this info from api doc?

Thanks for all of your help in advance. I really hope my question doesn't sound too silly:)