Boris Johnson has outlined his plan to the European Union (EU) to avoid a hard border between Northern Ireland and the Republic of Ireland after Brexit.
Mr Johnson said the plan "removes the so-called backstop".
The backstop is the insurance policy negotiated by Theresa May and the EU. It is designed to avoid any physical border infrastructure, which it is feared would bring back memories of the Troubles, after Brexit.
It would keep the UK in the same customs territory as the EU, and Northern Ireland closely tied to EU regulations - until the UK and the EU reach a trade deal.
But it would stop the UK striking its own trade deals, which is why so many Conservative MPs, including Mr Johnson, oppose the backstop.
So, what is his alternative?
The government wants the UK to leave the EU customs union. This would mean Northern Ireland and the Republic of Ireland ending up in two different customs territories.
This means lorries entering the Republic of Ireland from Northern Ireland will need to complete customs declarations. This is to ensure the correct tariffs (tax on imports) are paid when UK goods enter the EU customs union.
Reality Check's Chris Morris: From the beginning the EU has struggled to see how Ireland and Northern Ireland can exist in different customs territories while keeping the border as open as it is now under all circumstances. They will argue that - in the absence of a future free trade deal - this proposal means the UK is breaking commitments it has made about the border. The UK counters that the backstop has already been rejected in Parliament three times, and something needs to change.
Instead of installing customs posts and other physical infrastructure at the Irish border, the UK says declarations should be done electronically.
The government says physical checks would still be needed "on a very small proportion of movements". Currently, about one in 100 consignments entering the EU customs union are inspected to check that the goods match the information on the declaration.
These inspections could be carried out at warehouses or "designated locations, which could be located anywhere in Ireland or Northern Ireland."
The government's proposal does not spell out what these "designated locations" would look like, but it adds there should be "a firm commitment (by both parties) never to conduct checks at the border in future".
If adopted, a border solution relying on technology and remote checks would be a first. The EU does not currently share a single border with a non-EU country where checks have been completely eliminated.
That includes Norway (not in the EU) and Sweden (an EU member) - which share one of the most technologically advanced borders in the world. Their main crossing point processes about 1,300 lorries a day, with each waiting 20 minutes on average.
The EU has previously rejected a customs solution that relies on technology.
Back in January, Sabine Weyand, the EU's director-general for trade, said: "We looked at every border on this Earth, every border the EU has with a third country - there's simply no way you can do away with checks and controls."
The government says that some small traders should be exempt from paying duty. However, the document does not address smuggling head on. In other words, what will be done to detect and prevent traders, who should be paying duty, from crossing the border without completing custom declarations first?
Reality Check's Chris Morris: The EU will see much of this as a rehash of previous ideas that it doesn't think will work. And many people will worry that unspecified "designated locations" could become targets for anyone seeking to undermine the Northern Ireland peace process. The EU will push back hard against suggestions that it needs to revise its own customs rules to suit the UK.
Regulations on goods
When it comes to the regulation of goods, Northern Ireland would keep to the rules of the EU's single market, rather than UK rules.
That removes the need for product standard and safety checks on goods at the border between Ireland and Northern Ireland, because both will be part of an "all-island regulatory zone".
But it creates the need for checks between the rest of the UK - which will not be sticking to EU single market rules - and Northern Ireland..
All agricultural, food or animal products entering Northern Ireland from the rest of the UK will have to go through a Border Inspection Post. That's a bit of infrastructure where goods can be physically examined and paperwork checked.
Manufactured goods in Northern Ireland would also have to keep to EU rules, and these goods would be checked "at the boundary of the zone" - presumably at crossings between Northern Ireland and the rest of the UK, on the Irish Sea.
Reality Check's Chris Morris: This is quite a big concession from the UK side - basically accepting that there would have to be quite intrusive checks between Northern Ireland and the rest of the UK for a number of years, on things like product standards and food safety. The EU has always said there have to be checks carried out somewhere, and both sides will try to deny any suggestion that this amounts to a new border in the Irish Sea.
Having Northern Ireland following EU rules for the production of goods over which it has no say is, as the document says, "a significant democratic problem".
As a result, it is proposed that the Northern Ireland Assembly and Executive will have to sign off on the plan before it takes effect.
The Northern Irish institutions will be asked to approve the plan again every four years, and if they do not then Northern Ireland would stop following EU rules one year later.
The Northern Ireland Assembly has not met since early 2017.
Reality Check's Chris Morris: The issue of democratic legitimacy is a crucial one, but it cannot be applied unevenly. The EU is likely to have a problem with anything which suggests that only Northern Ireland could have - in effect - a veto on this plan. The point of the backstop was to provide a legal guarantee to keep an open border under all circumstances. Being subject to approval every four years simply isn't the same thing. If Northern Ireland voted to leave this arrangement things like checks on food safety would have to take place at the Irish border.