code, clients could show more advanced effects and game menus than was possible in Quake II and the user interface for mods was entirely customizable. Unless operations which require a specific endianness are used, a QVM file will run the same on any platform supported by Quake III Arena. The engine also contains bytecode compilers for the x86 and PowerPC architectures, executing QVM instructions via an interpreter.Quake III Arena features an advanced AI with five difficulty levels which can accommodate both a beginner and an advanced player, though they usually do not pose a challenge to high-tier or competitive players. Each bot has its own, often humorous, 'personality', expressed as scripted lines that are triggered to simulate real player chat. If the player types certain phrases, the bots may respond: for example, typing "You bore me" might cause a bot to reply "You should have been here 3 hours ago!". Each bot has a number of alternative lines to reduce the repetition of bot chatter. The Gladiator bots from Quake II were ported to Quake III Arena and incorporated into the game by their creator - Jan Paul van Waveren, aka Mr. Elusive. Bot chat lines were written by R. A. Salvatore, Seven Swords and Steve Winter. Xaero, the hardest opponent in the game, was based on the Gladiator bot Zero. The bot Hunter appears on magazine covers in the later id game Doom 3. On August 19, 2005, id Software released the complete source code for Quake III Arena under the GNU General Public License v2.0 or later, as they have for most of their prior engines. As before, the engine, but not the content such as textures and models, was released, so that anyone who wishes to build the game from source will still need an original copy of the game to play it as intended. Mods Like its predecessors, Quake and Quake II, Quake III Arena can be heavily modified, allowing the engine to be used for many different games. Mods range from small gameplay adjustments like Rocket Arena 3 and Orange Smoothie Productions to total conversions such as Smokin' Guns, DeFRaG, and Loki's Revenge. The source code's release has allowed total conversion mods such as Tremulous, World of Padman, OpenArena, and Urban Terror to evolve into free standalone games. Other mods like Weapons Factory Arena have moved to more modern commercial engines. Challenge ProMode Arena became