What does 'after commencement' mean in the following sentence?

Question

I have some trouble understanding legal terms. I'll be very grateful to you if you could clarify the meaning of 'after commencement' in the first sentence of the British Nationality Act 1981.>1.-(1) A person born in the United Kingdom **after commencement** shall be a >British citizen if at the time of the birth his father or mother is - (a) a >British citizen; or (b) settled in the United Kingdom.

Answer 1

In this sentence, "after commencement" means that this act is applicable once the law is enacted.