Gamecloud has a piece on the moddability of Civilization IV
. The article goes into detail about the numerous levels at which content creators can change the game of Civilization. From the article: "The next level offers Python and XML support, letting modders with more experience manipulate the game world and everything in it. XML (eXtensible Markup Language) files can be edited in standard text editors or in special XML file editors that have ease-of-use features like a grid view. Editing 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."
This is a more detailed look at a topic we've discussed before
. Gamespot has a preview
of the upcoming title, as well.