
Kayaker Magic and I, with occasional other input, have been analyzing the viewer Character folder, which contains llm files, xml files and targa files. This is the set of files that defines the system avatar - armature, volumes, topology mesh for the body parts, and morphs. Morphs include creating a male avatar from the default female, appearance sliders for shape, clothing, skin, hair and eyes, animatable morphs, and physics morphs.
We only work on it from time to time as there is no funding, very little interest from viewer devs, and there are more entertaining and lucrative ways to be creative. But it's worth doing if ya like this virtual world platform. We occasionally upload stuff to the RuthAndRoth github, hosted by Ai Austin who came up with our working project name: R3. Licensing as yet to be determined.
The system "classic" avatar aka Character was designed by Linden Lab with a first release c. 2005. A few upgrades since, including the added Bento bones in 2016. The original code, builds and artwork is inconsistent, has many errors and was not well documented. All of the original devs who worked on it are gone, and the various descriptions of it now range from "spaghetti" to "voodoo".
Ultimate goal: make a better system avatar for opensim grids.
Here is the latest update, for those who are interested in this expression of avatar geek.

https://github.com/RuthAndRoth/R3/issues/2