And enforced as such - just like you cannot have your macOS password be the same as your Apple ID password.
Huh, yes you can? http://osxdaily.com/2015/03/24/use-icloud-password-as-mac-lo...
I didn't know you could later enable it.
Sure it's not. But that doesn't mean it doesn't exist/is not possible :)
And enforced as such - just like you cannot have your macOS password be the same as your Apple ID password.