OptionalinferredOptionalisOptionalisThe name is an S4 method the package registered (its NAMESPACE exportMethods()): it is exported because
the package answers a generic for one of its classes, not because it defines a function of its own.
The S4 counterpart of isS3Generic/s3TypeDispatch.
Optionals3
The name is an S4 class the package owns, i.e. its NAMESPACE lists it in
exportClasses().