The EU divorce deal before the British parliament on Friday makes a few subtle but potentially consequential changes to the one Prime Minister Boris Johnson struck with Brussels in October.
Here is a summary of the accord, the final approval of which should help the British premier meet his pledge to "get Brexit done" on January 31.
The post-Brexit transition period would run to the end of 2020, during which time things would stay pretty much the way they are now. It could be extended by another year or two if agreed by both sides.
But crucially, Johnson inserted new language into the bill before parliament that prohibits London from seeking an extension should the sides fail to reach a comprehensive new trade agreement in time.
Analysts note that little prevents Johnson from pushing a new law through parliament removing that firm deadline should negotiations veer dangerously off track.
But it could prove to be politically costly for Johnson, and both sides want to move on to other issues more than three years after Britons first voted to leave the bloc.
Johnson's last-minute changes also remove parliamentary oversight of the negotiation process, with ministers no longer obliged to report back on progress in the talks.
Arrangements for the UK province of Northern Ireland were the trickiest part of the new deal, which replaces one Johnson's predecessor Theresa May failed to get through parliament.
The new protocol stipulates that Northern Ireland remains in Britain's customs territory, but in practice there would be a sort of customs border between the province and the mainland.
That is because of a hybrid system under which goods arriving and staying in Northern Ireland from non-EU countries will come under British customs rules, while those going on to the EU via the Republic of Ireland will come under the EU system.
Northern Ireland would keep aligned with the EU on a limited number of standards so food, animals and permitted industrial goods can more easily cross into or from the Irish Republic.
British authorities would have responsibility for the checks. But the EU has the right to have its officials present too to ensure the application of EU rules.
Britain and the EU agreed there should be "democratic consent" by Northern Ireland on the dual-rule customs system.
A simple majority in the province's assembly would have to vote for its continuance every four years, or eight years if there is sizeable cross-community support.
If the vote fails, the protocol would cease to be applied two years later, giving both sides time to try to come up with a workable alternative.
This voting requirement comes into force four years after the end of the transition period.
Value-added tax was a technically difficult point that was only resolved in the last few hours of the talks in Brussels. Differing VAT regimes would have contributed to the need for a hard border between Ireland and Northern Ireland -- something both sides said they needed to avoid at all costs.
EU rules on VAT are therefore to continue in Northern Ireland, but British customs officials would be in charge of applying and collecting them.
The EU notes that it compromised on its previous divorce agreement with the UK by dropping an insistence that Northern Ireland remain in the EU customs area -- the heart of the previous "backstop" which was so unpopular in London.
It also adopted the consent provision for the Northern Ireland Assembly, and along with it a way to end the protocol instead of having potentially indefinite application.
On the other side, the UK conceded on allowing customs checks between Northern Ireland and the rest of the UK.
It also dialled back its original Northern Ireland consent proposal by agreeing to a simple majority vote in the assembly, instead of what would have amounted to a right of veto to pro-British unionists.
It also agreed to Northern Ireland being subjected to a degree of EU oversight.
