If you've ever created a Ruby on Rails application, you've used AttributeMethods. These two modules -- one in ActiveModel, another in ActiveRecord -- are included in every model in your application, their methods called every time you read or write to an attribute. Given their importance, you would think there would be a lot of information about them out there, but actually there's very little.
https://kichijojikaigi.doorkeeper.jp/events/66983
https://github.com/rails/rails/pull/30895