ABCL structure identification

In order to be able to hack on ABCL a bit easier, asked Peter for a
description of the structure of ABCL. Unfortunately, there's no such
document nor did he have time to create one.

One of the first things I'd like to do in my new role is to get the
program structure clear. In my experience, that's the prime
prerequisite to be able to hack on a program oneself, but even more
when asking others to join in.

The idea is to create an HTML document which describes ABCL's
structure from different perspectives. What we're looking for now is
people with insights into the internals of ABCL or those who want to
get acquainted with the internals 

Among the things to be described in the document could be:

* General overview
* Which components are Java
* Which components are Lisp
* Interpreter vs Compiler
* Compiler stages/components descriptions
* Lisp type representation
* <which parts are not implemented? what needs doing?>
* ...

Any additional ideas of what needs to be made explicit would be
greatly welcome! Of course, a helping hand in finding out or getting
it described somewhat clear is very valued too. Anybody here with
knowledge on any of the items above? Or maybe someone who knows some
items which needs adding?