From English Common Law, a person must be born BOTH within the dominion of the sovreign AND under a single solitary allegiance to that same sovreign.
If a person is born whose father had a foreign allegiance and then the father subsequently naturalizes - the person is a citizen, although not natural born.
If that person then has children - born within the sovreign's dominion and under his allegiance, the children ARE natural born.
That is - the son of the naturalized father is merely a citizen, but the grandchildren of the naturalized father are natural born citizens.
The Wong court disagreed, as does virtually every other constituional scholar alive today.