As I understand it, all enhanced sharpness is a by-product of localized developer exhaustion. The developer in a highly exposed area will exhaust faster than the developer in an adjacent weakly exposed area. Because the developer chemicals are in solution, the unexhausted develper in the weakly exposed area will migrate to the strongly exposed area slightly. This increases the edge density of the strongly exposed area and reduces the edge density of the weakly exposed area.

Agitation re-distributed the developer concentration throughout, and thus minimizes the sharpness enhancing.

So, all developers rely on partial exhaustion for sharpness enhancing, when they are used for this effect. It does require that you not agitate too much (stand development being the ultimate in this approach). And developers (such as undiluted D76) won't provide the effect when they are too active to allow exhaustion. This commonly results in uncontrolled highlight density (i.e., burned out highlights).