Mask_texture from the (Rock-cave demo)

Hi all,

I’ve been looking into the M_cave_Rock material (mask) that ships with cave demo.
it uses a T_cave_Rock_large_M (mask texture)

And I’m wondering what the R|G|B|A channels are doing in this texture?

-red (looks to me its grunge texture)
-green (looks like specular)
-Blue (AO? )
-alpa (some stroke or/detail texture)

Is this correct?

Many thanks decor