Civilization IV is much more open to modification than its predecessors were. Game data and rules are stored in XML files, and a Software Development Kit was released in April 2006 to allow customization of game AI. The map editor supports Python. The World Builder allows a player to either design a map from scratch or edit a preloaded template map as a starting point for a new game. The player can modify the map by placing and modifying any number of rivers, landmasses, mountains, resources, units, and cities, as well as their attributes such as Culture generation. The World Builder for Civilization IV is in-game, in contrast to previous Civilization games where the Map Editor was an external application. 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 "[e]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." The Civilization IV software development kit was released on April 13, 2006, to coincide with the release of the v1.61 patch. The kit allows players to view, modify, or even completely re-write the game's DLL source code, enabling the modification of the game's AI and other integral parts of the game that were previously not accessible. Production Production and development The game engine for Civilization IV was built entirely from scratch, with some help from NDL's Gamebryo engine. This decision resulted in a full 3D immersion of the game, which was the first in the series, and which allowed easier readability and smoother, more in-depth zooming capabilities. Some of the quotes relating to the technology tree and narration for the game were provided by Leonard Nimoy. The soundtrack for the game features compositions of Medieval, Renaissance, and Baroque origin, and design for the title music was influenced by The Lion King. Composer Christopher Tin wrote the opening theme song "Baba Yetu" (Swahili "Our Father"), a rendition of the Lord's Prayer, which was performed by Stanford University's Talisman A Cappella. The song, when rereleased, became the first piece of video game music to be nominated for and