The Definition of a Server Language Class
named lists of the server language fields and methods to be exported
named list of the server class methods that are "operator overloading" of functions.
the names of any fields that should be made read-only in the R class
Chambers, John M. (2016) Extending R, Chapman & Hall/CRC. ( Chapter 12, discussing this package, is included in the package: ../doc/Chapter_XR.pdf.)