For information on converting to InterSystems IRIS, see the
InterSystems IRIS Adoption Guide
and the InterSystems IRIS In-Place Conversion Guide,
both available on the WRC Distributions page (login required).
Subclass should override this method.
The method is passed a stream object to which the output should be written.
Subclass can also return a checksum for the output.
Ths checksum is used to check to see the output is up-to-date.