code: @Override
      public void validateDefault(InputProblemReporter rep, boolean normalize)
          throws XMLStreamException
      {
          String def = validateDefaultNmToken(rep, normalize);
          if (normalize) {
              mDefValue.setValue(def);
          }
      }
docs: Method called by the validator
  to ask attribute to verify that the default it has (if any) is
  valid for such type.