Microsoft XML crazed fever extend to games.
Microsoft Combat Flight Simulator 3 and Age of Empires 3 had all the game variables in XML files.
Things like "points of contact" of aircraft. 3 points with Z= 0 are the landing gear. Delete all the others and enjoy your nigh-invulnerable plane. Delete these 3 and watch the airplanes cross the airfield floor and explode when they go underground, even before the game begins.
Age of Empires 3 had all the variables spelled out, like TrebuchetAttackForce = 20 or something like that. Replace that 20 with 255 or 65536 and watch all your enemies buildings crumble beneath a single catapult attack. But I think that on AoE 3 only the heroes were identified, so if you changed one of these generic attack units, they would change for BOTH sides, so you could mod your game to your heart's content, knowing that your enemies would get the upgrade too... with hilarious results.