Nkuvu,
See
What XML generators are currently available on PerlMonks?. There is a node attribute for the last update and/or edit time. I remember having a conversation about this years ago with
tye as a means for making an efficient thread watcher to let you know when the content of a node in a thread you were interested in had changed. I don't remember the exact details but as far as I know, the attribute is not updated when a node is modified (IOW - it doesn't work).
Not being a devil, I can't say for sure but I would think that could be used as a stepping stone. Unfortunately, as far as I know - that has never been fixed.