With help from James Strachan, who very quickly corrected a problem with Groovy's SAXBuilder, GroovyMarkup now works in Cocoon via the ScriptGenerator (BSF block).

Makes for a very nice syntax to generate XML:

xml.page() {
  content() {
  section() {
    title("GroovyMarkup test")
    p("Look ma, no angle brackets!")
    ul() {
    for(i in 1..5) {
    li("This is item " + i)
}}}}}

Way cool. Next step is to implement the Groovy SQL syntax.