module ActionController::ParamsWrapper::ClassMethods

def inherited(klass)

module is inherited.
wrapper key and attribute names. Called automatically when the
Sets the default wrapper key or model which will be used to determine 
def inherited(klass)
  if klass._wrapper_options.format.any?
    params = klass._wrapper_options.dup
    params.klass = klass
    klass._wrapper_options = params
  end
  super
end