Instead of being applied to the vertex, the renderers of the layers are mapped through 3D space in volumetric; allowing you to control the intensity of each of them thanks 3D position, rotation and scale parameters.
Using Triplanar Mapping
as renderer type for 3D Texture, the differents renderer are mapped through 3D Space.
In this case, with 1 uniform with single color for the front, left and top axis:
3D texture act like this:
Thanks this kind of texturing, you are able to control the mapping thanks 3D parameters like this: