Select an object. > Modify panel > Modifier List > Object-Space Modifiers > Projection modifier > Geometry rollout > Choose target geometry > Projection rollout > Click Add. > Click Project. > Projection Holder is applied to the target geometry.

The Projection Holder modifier appears for objects being used by the Projection modifier's Project Mapping feature. It contains the data generated by the Project Mapping operation, much as UVW Mapping Add or UVW Mapping Clear do for Channel Info manipulations.