How array is scanned trough on "for each xyz" exactly?

Hi there, I have a question about array checking. If I remember correctly on xy plane it goes by column: x1 -y1,y2,y3, x2-y1y2y3 etc. But how does it check when z is included, because this gives me most trouble? How exactly those loops work? Thanks

You can answer your own question by using the Browser to log each iteration:

Hit F12 in the browser and you can see exactly what the pattern is.