Microsoft just released the XPS Specification and Reference Guide today (Sep 13th 2005): http://www.microsoft.com/whdc/xps/default.mspx
There are three new specifications for download:
- Open Packaging Conventions which describe the methods for packaging information in a file format.
- XML Paper Specification which is a new general-purpose document format
- Windows Media Photo Specification, which is a new file format for continuous tone still images