Prefabs

Chisel works with Unity prefabs. A prefab can hold brushes, generators and composites, and what they add or cut out happens in the level you place the prefab in.

A window or door prefab can carry its own hole: a Hierarchical CSG composite with a subtractive brush for the opening and additive brushes for the frame. Drag it onto a wall and the wall gets its hole with the frame in it; move it and the hole moves with it.

A prefab can also hold a whole model. When it's saved, the meshes the model generated are saved in the prefab, so its instances draw them without building anything and without showing overrides. An instance whose geometry you change builds its own meshes; the prefab's stay as they are. The prefab only keeps the meshes it uses, so saving it again and again doesn't make it grow.