attr :location_string

Hi,

I have come across attr :location_string inside a class definition in
Rails application.

class Web < class Params
  attr :location_string

  def ....
  end

  ....
end

I know how attr_accessor, attr_reader or attr_writer works.
But I don't have any idea on attr in Rails.

Can you kindly explain what it does?

Thanks,
Christopher