# 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