We’ve just added a page of documentation about the Ubiquity parser to the Mozilla wiki. It explains the algorithms used, with lots of examples and links to particular functions in the source code. It will be of interest to anyone who wants to hack on the command-line interface of Ubiquity, to try out new features or to make the parser smarter.
There are still a few TODOs where we need to fill in some details, but we hope what’s there will be useful to someone. Let us know if there’s a particular feature/class/function that you’d like to see further documented or explained.