    # File lib/rubygame/event.rb, line 296
                    def initialize(pos,button)
                            @pos = pos
                            if button.kind_of? Integer
                                    @button = button
                                    @string = Rubygame::Mouse::MOUSE2STR[button] #a string or nil
                            elsif key.kind_of? String
                                    @button = Rubygame::Mouse::STR2MOUSE[key]
                                    if @button != nil
                                            @string = button
                                    else
                                            raise(ArgumentError,"First argument of MouseUpEvent.new() must be an Integer Mouse button indentifier (like MOUSE_LEFT) or a String (like \"left\"). Got %s (%s)"%[button,button.class])
                                    end
                            end
                    end