Not much is known about this file type other than it’s association with Object Brush (.orb) format. Presumably this format could be utilized in a way you can “paint” the map by barrowing small blocks containing tre2, htre, etc. Custom locations and terrains may be applied through manipulation of this file type.

Theories

Simple working theory is that the reason why these file types share the same structure is because they were key level editor objects, so the designer responsible for designing the back-end for map design must have engineered these files.