I have read these tutorials, I also have tried myself their examples which were very helpful.
I just read the DOM Navigation tutorial and I think it will return the previous brother of oNode and not the Parent, which is called previousSibling if I'm not mistaken.
If this is correct, if oNode is number 1 child as you said in a previous post (like i imagined it in the picture), this means that there will be an error, right?