Conceptually, Cocoatron is a combination of XProc and Apple's Automator application. XProc is the W3C's spec for high-level descriptions of XML processing pipelines. Automator is Apple's graphical application for creating scripting pipelines with drag-and-drop simplicity.
Cocoatron consists of six Automator Actions (composeable, configurable pipeline stages):
Much like SXPipe, these actions deal strictly with XML Infosets. An Infoset is constructed using Load XML Documents and serialized back to text using Serialize XML Documents. To create pipleines, place other, built-in Apple Actions before and after these two such as Get Specified Finder Items, Get Specified URLs or New TextEdit Document.
Implemented using the powerful libxml2 framework, Cocoatron includes support for XInclude, XSLT 1.0, EXSLT, XQuery, and validation against DTD, W3C XML Schema, and RELAX NG XML syntax. Under the hood, the XML Infosets created and returned by Cocoatron Actions are actually libxml2 xmlDocPtr objects.