The code can be obtained several ways, including directly by extracting files from the game code, using tools already in the game. See also Extracting WoW user interface files.
Viewing UI code by extracting game files
- The WoW game itself can export the user interface code and artwork files using in-game developer console commands, which are: 'exportInterfaceFiles code' (or 'exportInterfaceFiles art' for art). See Extracting WoW user interface files for detailed instructions.
Viewing UI code on the web
- wow.tools - a very up-to-date collection of various WoW game data, including the WoW user interface files. Files can be searched by WoW build and downloaded, or even compared on-line.
- townlong-yak.com - a database of all versions of FrameXML online. You can compare different versions to each other, view the contents of specific files (in a specific interface version), or just download the entire interface as it looked for a given version. Even test server versions are available.
- As of Patch as of 4.0.1, Blizzard's Interface AddOn Kit is no longer updated, and is replaced by extracting from the game itself.
World of Warcraft Interface AddOn Kit (US, EU) on Battle.net Support site held updated FrameXML files and in-game UI artwork, used by the actual game, for use by AddOn developers, community sites, or whoever was curious. See Interface AddOn Kit and 'Green Post': Updated FrameXML Extraction for more information.