_bump Extension?

[Pringles Man]

I found this little obscure extension for a few textures used in conjugation with gloss, luma, norm, etc. Anyone know what this does and to what extremes you can take it (I'm guessing it's like _norm, but less powerful)? From what I've seen, it's just a desaturated normal map with contrast filters.

[Spike]

its just a heightmap. it automatically gets converted into a _norm texture at load. there's no point providing both.

[Henry]

Pringles Man, the readme of darkplaces says it even get skipped when a _norm is found:

_bump.tga : bumpmap (not loaded if normalmap is present)