Neat! I think I get most of it, will have to read it a second time from home while also looking at the code
I figured there was something about generating a 2D thing first, then using something 3Dish for fancier stuff like caves and overhangs. Are the biome definitions generated separately, so that "map" can be used to amplify/decrease density? I recall seeing a colored map somewhere.
Interested in more for sure, especially on caves and rivers. I'm imagining using existing density/biome info to generate another map for geology. Although there you get into veins of different materials, instead of block or not, along with a desire to geographically separate some rare materials, hmm.