OK, the Evelyn Wood read of this seems to say there is some red tape but the bottom line is the document is not a must follow, it's advisory at the pleasure of the court.
No, it is a must follow because I have litigated them. Generally it is when someone is terminal and alert and they make a decision to stop treatment an let the cancer take its courts. The mother or father tries to step in over the objections of the husband or wife who is the named surrogate.
They are emotional gut wrenching cases but those are cases where intent is well documented, one even used a video in addition to the papers but the mother still would not let her son go. She did not trust her daughter in law.
As my experience indicates, they can TRY and dispute it but it is very hard to overcome.