I’m currently working on a exporter for my own file format and a skeletal simulation. But I’ve some problems to understand the Python data for bones:
head: This Bone’s “head” ending position when in rest state.
loc: This Bone’s location.
quat: This Bone’s quaternion.
roll: This Bone’s roll value.
size: This Bone’s size.
tail: This Bone’s “tail” ending position when in rest state.
… more 
Are some of this fields redundant and only another data representation? Are there any internal Blender docs that help me to understand the bones data? For example how could I calculate the absolute space coordinate of a bone?