nsxml is mostly deprecated in the newer versions of oacs (5.x), so there's no need for you of it. Anyway, its the former xml parser that we used to use at openacs, now it has been changed by tDOM because its amazing performance. More info here:
https://openacs.org/forums/message-view?message_id=103824
https://openacs.org/forums/message-view?message_id=95400
