public MODEL build(ConfigModelInstanceFactory<MODEL> factory, Element spec, ConfigModelContext context) {
        MODEL model = factory.createModel(context);
        doBuild(model, spec, context);
        return model;
    }
Builds an instance of this component model.
This calls instantiate(...), instance.setUp(...), doBuild(instance, ...).

@param factory A factory capable of creating models.
@param spec the XML element this is constructed from
@param context A context object containing various data used by builders.
config-model/src/main/java/com/yahoo/config/model/builder/xml/ConfigModelBuilder.java