def add(o)
      case o
      when nil
        raise Error, "Cannot add '#{o.class}' to window!"
      when Array
        o.each { |x| add_object(x) }
      else
        add_object(o)
      end
    end
def add(o)
      case o
      when nil
        raise Error, "Cannot add '#{o.class}' to window!"
      when Array
        o.each { |x| add_object(x) }
      else
        add_object(o)
      end
    end
Add an object to the window