Man! What a good answer. I just have one thing to add.
Sometimes, Blizzard's official copy of the FrameXML bundle lags behind a bit - in fact, when 1.9 went live, the bundle was broken for about a week.
When that happens, you can make your own bundle using
WinMPQ.
STRONG PRECAUTIONARY NOTE: WinMPQ likes to rearrange the contents of a file that it is browsing. This causes awful reactions in World of Warcraft. Several menus may stop working, and label text will vanish. To avoid this, always copy the MPQ files that you want to view some time before you open them with WinMPQ.
The location of the FrameXML bundle is:
C:\Program Files\World of Warcraft\Data\interface.MPQ
Remember: Copy this file before opening it. It can be rewarding to look in these bundles, but they are fragile.