No, it isn’t in written law, because it is based on self-evidence.
That’s why so many people are whining. “Why isn’t this self-evident definition in written law?” The answer is as simple as it is telling. Natural Law, as in my post, cannot be trumped by man’s law, common law, or any other written law.
There certainly are portions of natural law that have been incorporated into written law. I just don’t see how a good definition of NBC could be derived from any of the theories of Natural Law.
The only self-evident definition I can see is citizen at birth. I think it’s also self-evident that a free people has the right to determine (via their elected leaders) the details of who is granted citizenship at birth.