Fill and how it really works?

All, Im trying to get my mind wrapped around how fill actually works.
Lets say I have a new drawing.
I draw circles , and more circles within the same circles. lets say 10 of them all offset by say 10mm
and lets say
1:I want to fill every other circle. creating a bulls eye of sorts.
2: I want to fill every 3rd circle.
3: just fill one of the circles.
How does Light burn decide where to start and where to stop.

Thanks. -Sam

Have a look at this:

All shapes on a single cut layer are treated as though they are boundaries for a single object. Fill works by toggling on / off every time you cross a boundary - that’s really it.

This is why two shapes perfectly on top of each other will cancel out - crossing a boundary twice in the same moment turns the fill on, then off again all at once.