W3C:

2008-08-14: The XML Processing Model Working Group has published the Last Call Working Draft of XProc_ An XML Pipeline Language. This specification describes the syntax and semantics of XProc_ An XML Pipeline Language, a language for describing operations to be performed on XML documents. A pipeline consists of steps. Like pipelines, steps take zero or more XML documents as their inputs and produce zero or more XML documents as their outputs. Comments are welcome through 26 September. Learn more about the Extensible Markup Language (XML) Activity. (Permalink)