Verbosio is an architecture for XML language-specific editors to cooperate and edit XML documents in general. If you want to edit XUL in a XHTML editor, you're typically stuck unless that editor supports MathML editing as well. Verbosio aims to change that, by allowing specific editors to work together, and moving common tasks into the core architecture.
This project is under heavy construction, so don't expect anything soon. There's a lot of infrastructure going on in the Templates repository. Please, be patient.
The source code here is available under Mozilla Public License 2.0, GPL 3.0, and LGPL 3.0.
The wiki uses Markdown syntax.