It's local bleaching. It's easy to do. I used to use it when I was into gelatin silver printing. You make a very weak solution of potassium ferricyanide, with the print in a non hardening fix (I mixed it from scratch), pull it out, and brush the bleach on the area you want to lighten, rinse with water so that bleaching doesn't get away from you, repeat. Then stick print back in tray of fixer. Repeat process. I believe AA called it liquid light, or Zone system in a bottle...
Not all papers bleach the same. Forte Polygrade V was wonderful (long gone now, though), and Ilford MG IV would stain yellow if not careful. I only ever used fibre-based papers... Best to practice on discarded prints.