static void MVVarargs(ArgStruct args[], va_list varargs)
    {
      args[0].key = MPS_KEY_EXTEND_BY;
      args[0].val.size = va_arg(varargs, Size);
      args[1].key = MPS_KEY_MEAN_SIZE;
      args[1].val.size = va_arg(varargs, Size);
      args[2].key = MPS_KEY_MAX_SIZE;
      args[2].val.size = va_arg(varargs, Size);
      args[3].key = MPS_KEY_ARGS_END;
      AVER(ArgListCheck(args));
    }