Or you change it and respond with “You were warned”.

I seriously do not get this take. People use reflection and all kinds of hacks to get at internals, this should not stop you from changing said internals.

There will always be users who do the wrong thing.

> If you "just" rely on them not to do that, then your internals will effectively be frozen forever.

Or they will be broken when you change them and they upgrade. The JavaScript ecosystem uses this convention and generally if a field is prefixed by an underscore and/or documented as being non-public then you can expect to break in future versions (and this happens frequently in practice).

Not necessarily saying that's better, but it is another choice that's available.

Not everyone has to follow the MS approach of not breaking clients that rely on “undocumented” behavior. Document what will not be broken in future, change the rest and ignore the wailing.

It’s antithetical to what Zig is all about to hide the implementation. The whole idea is you can read the entire program without having to jump through abstractions 10 layers deep.