Member uscxml::DataModelImpl::addExtension (DataModelExtension *ext): This is currently unsupported
Member uscxml::DataModelImpl::isDeclared (const std::string &expr)=0: Is this still used?
Member uscxml::Debugger::_sessionForInterpreter: : We ought to change form InterpreterImpl to Interpreter everywhere
Member uscxml::IOProcessorImpl::create (IOProcessorCallbacks *callbacks)=0: We will eventually introduce callbacks and prevent complete access to the interpreter.
Class uscxml::X: : More performant XercesStrings https://alfps.wordpress.com/2010/05/27/cppx-xerces-strings-simplified-by-ownership-part-i/