Yes, topology is it exactly!

> You say "side pieces" it's well the "sides faces" not the "edges" side?
> (due "only delete edges if they are not attached to something")

Yes that is correct, the side faces must be deleted first. This leaves open edges and then the open edges can be deleted.

But I just realized that there is a bug that if deleting the edges causes the object to become a fully closed solid (like in this case), there is a problem with the structure of the object which may interfere with some operations like booleans. The problem will be solved if you save the file and re-open it though. So until I get a chance to fix this bug you may need to save the file and re-open it after you delete holes in this manner.

Otherwise you may notice some strange problems like booleans not handling the interior parts of objects properly.


> But something will be very cool in this case (and useful in many other cases of
> course) : a "loop (or ring) selection" faces (or edges) :)
> Is that possible?

Yup, it was part of your previous list! Sometime after array and image planes are functioning.

- Michael