The docmodel code base is going to undergo some tidy-up for its next version (0.2.0) which will change its structure and interfaces. As such, I'm going to forgo adding developer guides until 0.2.0. That said, if you do want to dive into the code, it should be relatively simple for you to find your way around. You can find the source on BitBucket, and you can keep up to date on progress by watching the next branch.
Contributions in the form of code, bug fixes, etc. will always be welcome!