The engine supports the concept of "occluders". An occluder is usually a box-shaped object that is placed inside other more complex geoemtry or behind it, to speed up rendering. For example if you have a wall, and behind it a big number of objects, will be good to place an occluder object inide of that wall. Occluders are used when dynavis is used.
To define an occluder object you just have to name it with the prefix "_occ_".
It's best if you use "Box" objects instead of "Editable Mesh" objects, so it will be used in the engine as a native element of type box.