allow root collections

Currently, root collections are not supported.

Example:

```
[#gadget]*!:uuid:ex.01
[#gadget]*!:uuid:ex.02
[#gadget]*!:uuid:ex.03

([#gadget])(*!:uuid:ex.01)
([#gadget])(*!:uuid:ex.02)
([#gadget])(*!:uuid:ex.03)
```
