The root component is considered as an ID space, so getFellow and wire will work

If components don't attached to a page, it is hard to find the fellows unless the root component is an ID space. It is more convenient if we consider the root component always being an ID space.

Challenge:
1) performance
2) shall the root component be an ID space once it has been attached to a page? If not, it is a bit inconsistent. If yes, it might have some backward compatibility issue.
Conclusion: it is better to be compatible.