help.rb

    def update_unbound_check_box(attrs)
      boolean = attrs[:boolean] || (attrs[:on] && attrs[:off]) ? true : false

      case
      when attrs.key?(:on) ^ attrs.key?(:off)
        raise ArgumentError, ":on and :off must be specified together"
      when (attrs[:boolean] == false) && (attrs.key?(:on))
        raise ArgumentError, ":boolean => false cannot be used with :on and :off"
      when boolean && attrs.key?(:value)
        raise ArgumentError, ":value can't be used with a boolean checkbox"
      end

      if attrs[:boolean] = boolean
        attrs[:on] ||= "1"; attrs[:off] ||= "0"
      end

      if attrs[:checked] || (attrs[:on] && attrs[:on] == attrs[:value])
        attrs[:checked] = "checked"
      else
        attrs.delete(:checked)
      end
    end