1. In the second edition, chapter 7: "Blizzard has provided us with a tool to extract the XML files that comprise the default user interface. To extract it, you must download the User Interface Customization tool from http://www.worldofwarcraft.com/ui."

    It seems like this link is out of date. I found this: https://us.battle.net/support/en/article/download-the-world-of-warcraft-interface-addon-kit and I think it has the same content (though you have to move it yourself to your WoW directory).

    Hope this helps!

    UPDATE: I think you get these files in the right directory (plus two other folders) if you follow the steps here: http://www.wowwiki.com/GettingstartedwithwritingAddOns

    The process has changed. Instead, you need to do the following:

    1. Run the WoW executable with the -console switch. For Windows this is wow.exe -console, but for Mac OS X you'll need to run something like open 'World of Warcraft.app' --args -console.

    2. Once the game has been loaded, press the tilde ~ key to open the console. Run the ExportInterfaceFiles code command to extract the FrameXML code. You can run the ExportInterfaceFiles art command to get the artwork.

    Either will extract into the WoW directory.

    This has been added to the errata for Chapter 7.