Here is the simplest way:
1. Create two rectangles in GH. One rectangle sits inside the other one just like a window sits inside a wall (co-planar).
2. Pipe them separately to Topology.ByGeometry
3. Use Topology.AddAperture and feed the "wall" as the topology and the "window" as the aperture topology (you may need to make it into a list if it is a single item).
Another thing to try is to make a CellComplex. Get all the faces, scale them around their own centroid by a fraction (e.g. Xscale = YScale = ZScale = 0.5). So now you have smaller faces that are co-planar with the original faces. Now use AddApertures and feed it the CellComplex and these new scaled down faces.
Thank you for the rapid response!
I managed to get output from Topology.Apertures with two co-planar faces as input.
With the cell-complex - no such luck. Does the aperture geometry have to be derived from the cell-complex geometry in some way, or should it suffice that i know that the geometries are co-planar?
Is it that you need to get to the faces before you can get the apertures?
Yes exactly. Apertures are the "children" of faces. "Contents" can be the children of any topology