You can view Blizzard's FrameXML and AddOns code and artwork by instructing the WoW client to extract those files, or by viewing them online.
Extracting interface files
Since the switch to the streaming download system in patch 4.0.1, the previously-used Interface Toolkit is no longer supported by Blizzard. Instead, the interface data and artwork can be extracted directly from the client (as of patch 4.0.6) by using the following console commands at the log in or character selection screens to extract the code and art, respectively:
ExportInterfaceFiles code ExportInterfaceFiles art
Once extracted, the files can be found in the "BlizzardInterfaceCode" and "BlizzardInterfaceArt" folders in the World of Warcraft directory. For detailed instructions concerning access to the console, see Console.
/consoleslash command, or via the real console while logged into a character: you will just get an "Unknown Command" response.