i understood the long stay visa differently: since you can spend the whole year in the EU there is no limit on traveling except he can't spend more than 90 days in any single EU country (besides the one he got the visa for), but even if that is wrong, if he gets the visa for the largest country to traverse, which i think is france, then he could: enter france, travel to another eu country, walk 90 days, go back to france, walk 90 days in france, travel to another EU country walk 90 days, go back to france, finish walking. if he still has a leg left at that point, wait until the 90 days are full, then finish the remaining leg. i don't know how much time he really needs, but i think the whole EU needs less than a year. 180days outside of france could be enough.

with "how would anyone know?" i meant the reverse. if there are no stamps that document the travel within the EU, how can he prove that he did not violate the rules?

all in all, these visa rules are way to complicated. it sounds like that without the EU existing, he would have had 90 days in each european country mostly visa free. so that is in effect a regression. as a EU citizen i am not happy about that.

i traveled across europe before the schengen area was created, and there was no problem entering any country and stay there other than some countries charging a lot for the visa at the border. anyone with a british or US or similar "powerful" passport would have been able to do the same.