WoW:Viewing Blizzard's WoW user interface code

• Download Blizzard's UI Customization Tool (Follow the Support Tools link on http://www.worldofwarcraft.com/ )
• Run it, click the appropriate button(s)
• When it's done look in Interface/FrameXML

Note: Old instructions for extracting the files before the release of the tool can be found here [1].