From searching around, it seems there was written documentation for the XIFF API at one point (possibly in beta3?), but so far I haven’t seen any sign of it. Am I too late to the party? Or is there any hope of getting started this late in the game?
I got frustrated with this too, but luckily I noticed that the sources have asdoc compatible comments.
After some struckle with Flex 2 SDK asdoc generations / Xiff bugs (don’t know which one), I managed to get somethingout.
http://paazio.wippiespace.com/xiff3doc/
I don’t promise to keep them up to date, but at least it is a place to start.