As I understand it, the backstop changes agreed by EU and UK negotiators would "protect UK from bad faith" by EU in negotiations over the coming two years on putting in place alternative arrangements either to replace the backstop or prevent the backstop ever being needed.
However it won't guarantee that the backstop could not be permanent.
So I really don't see how Geoffrey Cox could drop his formal legal advice of last November that "the protocol [which contains the backstop] would endure indefinitely until a superseding agreement took its place" and the "Withdrawal Agreement cannot provide a legal means of compelling the EU to conclude such an agreement".
So although what has been agreed, and will be announced by Theresa May and Jean Claude-Junker in a couple of hours, will be "legally meaningful", it surely cannot mean the prime minister would secure ratification of her deal by MPs tomorrow.
Because the majority of ERG Brexiter Tory MPs, perhaps 60 odd or more, would still vote against her Brexit plan.
That said the EU and UK government lawyers thought even on Saturday that the legal instrument they had tentatively agreed would have warranted a change of legal opinion as to the risk of backstop becoming permanent.
But Mr Cox disagreed, and we’ll see whether he still does.