URL where to find the error

Which section should be improved

Documentation says that this is the observed form field element, while it actually is a FieldObserver.
We can read its fields property to access the observed field(s), so it's not really broken, but the documentation is misleading.

How should this section be improved?

I'm not sure if the current behavior is intended. this being a FieldObserver feels a bit weird, but it offers more information that a singel field (or list of fields) would offer.

So, either:

Documentation needs to be updated.
If it's a bug in the API of up-observe, we should to fix that. :)