1. Page 132 of the 2nd edition says the current UI.xsd is located at

    http://wowprogramming.com/FrameXML/UI.xsd

    I don't think it is there. Where is it?

    It's most definitely there. It won't render in your web browser, but the file is there.

    Thank you. On a Mac, the page renders with Firefox but not with Safari.

    If you want to VIEW the file rather than use it as a source for validation you should just use the XML Browser. Otherwise you can unpack the version from your own WoW install using the Addon Kit, as explained in the book.