As of 2024-06-23, it is not clear whether the best policy is for this to inherit from 'oce' or to define itself here. Doing the former might seem sensible, since it might reduce the need for code here, but it seems to cause problems (e.g. inability to build vignettes in the standard way) that I have trouble understanding. We ran into similar problems in the argoFloats package too, and there we decided to define the object fully in the new package. For now, that's the approach used here also.