Stephane Bortzmeyer:
OP. In Atom, it seems to me that 2) is the only reasonable choice (1 or 3 would require to store the content - or at least a hash - and, if applied blindly, would create many false positives since a simple reformatting of the XML would trigger a "change").
Read my response again. Option 3 can't possibly trigger any more false positives than 2 since it requires option 2's conditions to be satisfied (i.e. the updated element changed) in addition to the content having been changed.
Regards James
