https://developer.apple.com/support/app ... erence.pdf
Initial reading made it seem like it's pretty detailed. The more I look at it, though, the more it looks like javadoc/doxygen generated content. Not as good as TN1150 (not 1050..) was for HFS+..
Anyway, I can now officially say lots more coverage (with much needed illustrations this reference doesn't have) will be in Volume II!