The future
Please feel free to link to this so people don't have to keep asking the basic questions and can start asking the deeper ones. One of the important deeper ones is: where should we go in the future? Since this format is becoming something of a de facto standard between window managers, should we set up some kind of freedesktop.org standards discussion? Would it be useful to spin off Metacity's theme parsing code into a separate, LGPL-licensed library so that other applications could use it more easily?
What would a version 3 of this format look like? Could we simplify the window / frame_style_set system? (I can imagine abolishing both, and being able to write <frame_style for="normal+unfocused+maximized">… and having Metacity assume it applied to all resize permissions and shadednesses.) Maybe we should try to do everything with SVG we can? Getting more wild and handwavey, is it worth keeping XML-like? Maybe if other window managers were dealing with the files, .ini-style files would be more universally useful? Or perhaps not. And then of course we need a decent graphical editor for it. I have a few ideas, but if anyone fancies jumping in...