Key points to note here.
1. You need to see the para cited by Jon (para 49) in context to appreciate its full force.
2. Start with para 43. This defines a hard border. No physical infrastructure or related checks. So not, even, 🇨🇭/ 🇫🇷 or 🇳🇴/ 🇸🇪. 
3. Then look at para 47. This basically says that N-S cooperation depends on “a common EU legal and policy framework”. Eg it depends on *a lot* of EU law.
4. So when you get to 49, you see the force of the commitment to N-S cooperation (which the U.K. accepts depends on a *lot* of EU law).
5. And the commitment on the border is to avoid any infrastructure/related checks.
6. And in default of solutions to operating a customs/regulatory border with no infrastructure (drones/blockchain/leprechauns) the U.K. is now committed to “align” so as to avoid such a border.
7. And also to “align” so as to preserve in NI the *lot* of EU law that the U.K. accepts underpins N-S cooperation.
8. And this commitment applies to all U.K., unless NI - all of it, in the form of a reinstated power-sharing executive, not just the DUP - agrees otherwise./end
PS NB that U.K. is recorded as leaving the “Internal Market and the Customs Union”. Para 45. But the capital letters may matter: “a customs union”; “an internal market”.
The U.K. may, formally, not be in either. But Rome under Augustus wasn’t, formally, a monarchy.
And the U.K. is pretty good at distinguishing the formal from the efficient in our constitution.
