Version 3.4.6 doesn't give up its class nodes in the same way.
These are not in the chain. One would have to search for them 
sequentially through all the nodes.

3.2.3 returns all the defined classes and structures, not just those 
that are used.

4.2.0 and 4.2.1


tus = structure(lapply(list.files( pattern = "tu"), parseTU),
		   names = list.files( pattern = "tu"))

lapply(tus, function(x) names(getClassNodes(x, "ABC")))