• active_support/core_ext/array/conversions
• active_support/core_ext/string/inflections
• active_support/core_ext/object/deep_dup
• active_model/error
• active_model/nested_error
• forwardable

• 模組 ActiveModel
• 類別 ActiveModel::Errors
• 類別 ActiveModel::RangeError
• 類別 ActiveModel::StrictValidationFailed
• 類別 ActiveModel::UnknownAttributeError