Thanks for the tip, nruddock! I've actually considered using something similar. Full XPath syntax would be quite the overkill here, but those libraries might come in handy for other things.

Implementation isn't really the issue here, mind you. Everything I've shown in my earlier post is already running, and any extensions one could possibly want for Poser files are almost trivial to add. The main question is, how to write down a path expression in the most user-friendly way. One string with an XPath-like syntax? A list of argument each of which represents one path component? Or an internal DSL using operators, possibly looking something like this:

doc "actor"
@ "head*" "channels" 
("indices"|"numbDeltas"|"deltas")
delete

(The forward slash "/" can't be used as an operator in Scala since it's already taken for comments. But the backslash "" is fine.)

-- I'm not mad at you, just Westphalian.