You can put multiple folder stacks into folder stacks no problem here. Even via key command.
How? I just tried it. I even tried creating a Folder Stack and dragging in another Folder Stack and it didn't work.. I know that you can have multiple Summing Stacks in a Folder Stack, that works fine. But you can't put a
- Folder Stack into a Folder Stack
- Summing Stack into a Summing Stack
- Folder Stack into a Summing Stack.