Basis of broadening Reissue is tested. Non prior art narrowing can be retrieved within a two years of issue if adequately supported in the specification. Enablement, ie, description sufficient to make and use, and best mode are all that is necessary. Again, correspondence between the specification and the claims is tested. This is a question where what is good for the goose is not good for the gander.
Indefinite language is always indefinite language even if is seems properly introduced.
Enablement, even a feeble one example enablement, is enablement. In the end, the scope of the claims may be severely limited because of a lack of supporting breadth for the claims, but that, as they say, is another issue for another day and is outside the purview of what the PTO is testing. This question tests enablement in contrast to bare utility. A single use may not be sufficient to enable. The tip off here is the need for undue experimentation for a person of ordinary skill to practice the invention.