I'm a newbie on this one but here's my explanation on the crossover technique..
2 ways....Way 1: Wind 1/2 the core..then yank that wire back over to the starting point. What results is a stupid looking wire that crosses the middle of the core. Wind the rest (properly).
Way 2: Have 2 windings on the core. Make the cross connection with a piece of wire so it's like way 1...(Sorry if that's sounds dopey..)
There were PDF's somewhere along this thread that had drawings that illustrated the form.
Normally on a fully wound single layer toroid the wire ends meet..(of course not short out.) Depending on the cct, there can be a large electric field hot spot... Arcing at the extreme. Alternative winding such as the crossover technique reduces the electric field strength at this spot. Sometime soon I'll be examining under what conditions the inductor resonance increases..
As someone mentioned...It's artsy... D from BC