External errors
Add errors from an external source to active model. Useful if you have validations that are not done by the model's validators.
Example usage
# Add errors from an external source to the model:
class SomeModel
include ActiveModel::Model
include ExternalErrors
end
some_instance = SomeModel.new
some_instance.valid?
#=> true
some_instance.external_errors << 'some external error'
some_instance.valid?
#=> false