Required Files
- singleton
- active_model/observer_array
- active_support/core_ext/array/wrap
- active_support/core_ext/module/aliasing
- active_support/core_ext/module/remove_method
- active_support/core_ext/string/inflections
- active_support/core_ext/enumerable
- active_support/descendants_tracker
Namespace
- MODULE ActiveModel
- MODULE ActiveModel::Observing
- MODULE ActiveModel::Observing::ClassMethods
- CLASS ActiveModel::Observer