Selection Mask
Selection Mask Node has a single parameter - a name of the polygon selection tag that can be used for object. This node will generate white color for polygons that belong the the specified selection and black otherwise.
Selection in Viewport and Render:
Decal Restriction
This selection node can be useful to restrict the appearance of decal to certain regions specified by polygon selection. The example below presents the selection mask combined with procedural decal mapping to let the decal appear alone on the single side of the shaderball.