More game attributes are stored in XML files, which can be edited with an external text editor or application. On September 20, 2005, Firaxis Games senior producer Barry Caudill stated that "diting these files will allow players to tweak simple game rules and change or add content. For instance, they can add new unit or building types, change the cost of wonders, or add new civilizations. Players can also change the sounds played at certain times or edit the play list for your soundtrack."