Use face material ID – When more than one material is applied to the different faces of the same object, Maya will internally create creates face IDs. If all those materials share the same VRayMultiSubTex, V-Ray will consider considers the face IDs when feeding the data (color or texture) to the materials.
Use object ID – The VRayMultiSubTex will consider considers the Object IDs of the object when feeding the data (color or texture) to the material.
Random by RenderID – The VRayMultiSubTex will assign assigns random colors based on RenderIDs (internally generated by V-Ray).
Random by node name – Generates a color index based on the name of the node that the texture is applied to.
Random by instance ID – The VRayMultiSubTex will assign assigns random colors based on the IDs of objects instanced with the particle instancer in Maya.
Texture Switch – Enables the Switch texture parameter to determine which texture will be is used in the material.
Switch texture – A floating point value that calls the texture from the Texture List (below in the UI) by the ID number.
Interpolate – If the switch value falls between two textures from the Texture list, this interpolate between them. Otherwise, when disabled, the closest texture from the list will be is used.
Add New Item – Adds a new sub-texture to the texture list.
Value – For modes that use IDs, specifies the ID that will correspond corresponds to each texture.