Multi attachments

I'm not sure if devs are aware of this, I wasn't.

If you are very precise you can force the game (no xml and no tinker panel needed) to attach a part to 2 attachment points at the same time. I'm not sure yet if this is possible with subassemblies (like a side booster attached to two decouplers at the same time, for example).

Here you can see an example of how it works. The long strut is connected to the top of the crew cabin and the square one to the bottom. No matter which one I remove the docking ports still attached to the crew cabin.
And here you've got a craft to try this.