The W3C XML Processing Model Working Group has published the candidate recommendation 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. An XML Pipeline specifies a sequence of operations to be performed on zero or more XML documents. Pipelines generally accept zero or more XML documents as input and produce zero or more XML documents as output. Pipelines are made up of simple steps which perform atomic operations on XML documents and constructs similar to conditionals, iteration, and exception handlers which control which steps are executed."
