What kind of Brexit delay, if any, would the European Union's leaders sanction, when the prime minister asks for one in a week's time, at the next EU Council?
Truthfully, no one knows.
Actually that is only half right. In the implausible event that MPs next week ratify the PM's Brexit deal at the third time of asking, they would grant her a couple of months' postponement of the moment we depart, so that legislative and technical preparations could be completed.
Just to be clear, I don't see how she wins. Too many Brexiter and Remainy Tory MPs hate her deal so much that they'll never be intimidated into backing it.
They will also be acutely aware that parliament risks being brought into serious disrepute if all the stale arguments that were rehearsed for hour upon mind-numbing hour during the two previous meaningful-vote debates are restated next week by the same predictable roster of characters and yet yield a different outcome.
This would not be democracy gilded by the power of reason.
It would be widely seen as the bankruptcy of parliament - a Commons tainted by the correct perception that MPs would be changing their minds at the last only because they would have been frightened into believing that a form of Brexit they see as bad for Britain may yet be better than an unknown alternative.
So the stakes for the UK could not be higher when the PM launches Meaningful Vote 3 after the weekend.
Now if I am right, and the PM loses that vote again, how would the EU react?
Well, my sources in EU capitals are clear and agreed on only one point.
It depends utterly on whether the PM asks for something specific.
For the avoidance of doubt, if she turns up and simple says "gimme a delay, but I'm not sure what I'll do with it", they'll "ask her for clarity" - according to one well-placed source - and "would not take any decision at all".
She would be sent home, and invited to re-submit her request for extra time at an emergency council of EU leaders the following week.
Yes, I am not making this up.
Active consideration is being given in Brussels to a crisis summit of EU leaders literally a day or two before the official Brexit day of 29 March.
In the words of another well-placed EU source, Brexit has "brought the need for a new word on what is beyond [or more extreme than] 'brinkmanship'".
All of which explains why, as per my earlier note, it is seen by many MPs as vital that they have by then started a practical and speedy process of coalescing around some or other version of Brexit or indeed a route to remain in the EU - as per the Benn/Letwin/Cooper plan I told you about a few hours ago.
And what about the PM's threat that if she asks for any kind of delay to rework or replace her own Brexit deal, that delay would never be short enough to avoid the embarrassment for Brexit Britain of having to participate in May's election to the EU parliament?
For what it's worth, my EU sources say she is right: they are (unusually) of a single voice and opinion that there will not and cannot be any Brexit delay - other than to implement a deal already ratified by MPs - which would be short enough to avoid what they see as the car crash of Nigel Farage standing again as an MEP.
Which may in the end be a prohibitive deterrent to British MPs and European Union leaders agreeing that the UK, its legislators and its people deserve a period of reflection to decide on a Brexit that binds rather than divides the nation.
So in the end what are the options?
There are three and a half.
The one and a half are a short extension to implement May's deal, if it's third vote lucky for her, either to 23 May or 30 June (juridical opinion is still divided about which of these dates obviates the need for the UK to put up EU election candidates).
The second option is a long delay, for May's deal to be fundamentally reworked or for a referendum.
The final one you will not need reminding is a no-deal Brexit. In Berlin, Paris, Madrid, Rome and Brussels, no deal remains a very real risk and threat - and could imminently become a choice if they lose all hope of the UK deciding what kind of Brexit, if any, it wants, and soon.
PS: Parliament just rejected the Benn/Letwin/Cooper amendment. This goes some way to restore the PM's authority - but it will be galling to the many members of her cabinet who oppose a no-deal Brexit.
Because without that amendment, the EU will legitimately query whether MPs have the ability to coalesce around any kind of Brexit or no-Brexit plan, as an alternative to the PM's.
Which means that if MPs reject a meaningful vote on the PM's deal for a third time next week, the default option of a no-deal Brexit becomes a very real risk indeed.