code: public void registerType(ModelElementType modelElementType, Class<? extends ModelElementInstance> instanceType) {
      QName qName = ModelUtil.getQName(modelElementType.getTypeNamespace(), modelElementType.getTypeName());
      typesByName.put(qName, modelElementType);
      typesByClass.put(instanceType, modelElementType);
    }
docs: Registers a {@link ModelElementType} in this {@link Model}.
  
  @param modelElementType  the element type to register
  @param instanceType  the instance class of the type to register