public void accept(@NotNull PsiElementVisitor visitor) {
   if (visitor instanceof YangVisitor) ((YangVisitor) visitor).visitNotificationStmt(this);
   else super.accept(visitor);
 }
 public void accept(@NotNull PsiElementVisitor visitor) {
   if (visitor instanceof YangVisitor) ((YangVisitor) visitor).visitMandatoryArg(this);
   else super.accept(visitor);
 }