XProc Test Suite
http://norman.walsh.name/2007/05/03/xprocTestSuite
"The nascent XProc test suite is now on the web."
XProc: An XML Pipeline Language
http://www.w3.org/TR/2007/WD-xproc-20070405#components
"An XML Pipeline specifies a sequence of operations to be performed on a collection of XML input documents. Pipelines take zero or more XML documents as their input and produce zero or more XML documents as their output."
XProc Implementation
http://norman.walsh.name/2007/04/18/xprocImplementation
"In the intervening months since I first mentioned my plans to implement XProc, I've ripped it apart and started over twice. Third time, it seems, really is a charm."