module IceCube::Validations::DayOfMonth

def day_of_month(*days)
  days.flatten.each do |day|
    unless day.is_a?(Integer)
      raise ArgumentError, "expecting Integer value for day, got #{day.inspect}"
    end
    verify_alignment(day, :day, :day_of_month) { |error| raise error }
    validations_for(:day_of_month) << Validation.new(day)
  end
  clobber_base_validations(:day, :wday)
  self
end