Image copyright AFP Image caption Demonstrators protest at the Carrickcarnon border crossing on the road between Dundalk in the Republic of Ireland and Newry in Northern Ireland

The Democratic Unionist Party's (DUP) bottom line has always been that any new Brexit arrangements should not separate Northern Ireland from the rest of the UK, economically or constitutionally.

Under the Stormont assembly's cross-community voting rules, contentious measures require a majority of both unionists and nationalists in order to pass.

That means that the biggest parties - the DUP and Sinn Féin - in effect have a veto.

The DUP had hoped to secure an upfront Stormont vote to approve the new arrangements.

But it's understood that the current proposals would give Stormont a say four years after the end of the transition period - that would mean 2024.

A straightforward numerical majority would keep the special arrangements in place for another four years.

Alternatively, if the arrangements get cross-community consent - in other words, if they're passed by most nationalists and most unionists - they would remain in place for eight years.

But a vote couldn't happen if the assembly wasn't operating.

Image copyright Reuters Image caption The DUP's bottom line has always been that any new Brexit arrangements shouldn't separate Northern Ireland from the rest of the UK

Presently, it hasn't sat for more than two and a half years, since Sinn Féin resigned from the power-sharing devolved government.

Shortly afterwards, an election left unionism without a numerical majority in the Stormont chamber for the first time in the history of Northern Ireland.

So for the DUP, the issue of consent - and a fear that Dublin and Brussels would have too big an influence on trading rules - goes to the heart of the party's concerns that Northern Ireland's place in the UK would be weakened.

Several rounds of talks to restore the Stormont Executive haven't succeeded - and few, if any, hold out hope that devolution is returning in the coming weeks.

What are the outstanding issues?

Sinn Féin and the DUP continue to essentially blame each other for the ongoing deadlock.

Sinn Féin vice-president Michelle O'Neill - who would be in line to jointly lead the Northern Ireland Executive with Arlene Foster if devolved government came back - has re-emphasised her party's opposition to any mechanism which would allow the DUP to block Brexit plans designed to keep the border open and prevent any disruption to trade across the island of Ireland.

Her tweet - "No border and no veto" - shows how the complexities of Stormont politics have become increasingly bound up with the UK-EU negotiations.

The technical talk about Brexit and the border focuses on trade, goods regulations, and potential tariffs.

But for politicians in Belfast and Dublin, the significance of those issues is generated by deeper issues - such as identity, nationality, and peacebuilding.