Private apis are nothing like public. You can’t just document them and toss em out the door because Private means you can change and break them every release without concern because you control all the consumers. You can also start using incomplete ones before the contract is solidified. Public means they are in use and shouldn’t change much, and if you do you need to announce a deprecation and then slowly deprecate. Not that apple has to do that but generally that is the rather large difference and you know the moment they break one everyone will be scream at them for that.