xsl extension fns in clojure.
See http://www.w3.org/TR/xslt20/#extension-functions
See http://cafeconleche.org/books/xmljava/chapters/ch17s03.html
Xalan: http://xml.apache.org/xalan-j/extensions.html
Saxon 9.1.0.8 is the last free version that supports extension functions.
Saxon <= 9.1.0.8: http://www.saxonica.com/documentation9.1/extensibility/functions.html
Saxon > 9.1.0.8: http://saxonica.com/documentation9.4%2Ddemo/html/extensibility/functions/
By CLI: see test.sh.
Programmatically, using JAXP: lein test. See http://en.wikipedia.org/wiki/Java_API_for_XML_Processing#XSLT_interface