[Rule Chain] How does nested rules queries work?

Didn't find the precise answer to this question in the Documentation, so let's go:

Does child rules are applied only to resulting customers of the Parent Rule?
Or does the child rules query results work independently of the parent's result?

Example: 100 customers

(A) Not Nested: 

- Rule 1 (20 resulting lines out of 100)
- Rule 2 (50 resulting lines out of 100)
- Rule 3 (10 resulting lines out of 100)

(B) Nested:

- Parent Rule 1 (20 resulting lines out of 100)
--- Child Rule 2 (5 resulting lines out of 20)
--- Child Rule 3 (3 resulting lines out of 20)

If it works like (A), then probably all child CTA rules will need controls so the CTA doesn't open over and over again.

Thanks,
Bruno