I'd normally be inclined to agree that minor things are probably good enough, but "absolute non-negotiable" is a rather strong wording and i think small things technically violate a facial reading, at least.

On the other hand, I did find what I think are the relevant docs [0] while looking more into things, so I got to learn something!

[0]: https://docs.adacore.com/gnat_rm-docs/html/gnat_rm/gnat_rm/c...

> except for some small things that are documented

I can't think of any established language that doesn't fit that exact criteria.

The last major language breakage I'm aware of was either the .Net 2 to 3 or Python 2 to 3 changes (not sure which came first). Otherwise, pretty much every language that makes a break will make it in a small fashion that's well documented.