Matteo Bruni (@Mystral) commented about dlls/d3dx9_36/d3dx9_private.h:
struct volume size; uint32_t mip_levels;
- uint32_t elements;
Those are usually called "layers" in modern 3D lingo, so probably `layer_count`.
(Ideally it should have been `level_count` right above it as well, like for example in wined3d. Alas I missed it at the time...)