public function setMetaGroup($group = null)
    {
        if (!preg_match('/^[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*$/', $group) && $group !== null) {
            throw new InvalidArgumentException("Provided group [{$group}] is not valid variable name.");
        }

        $this->attributes['meta_group'] = $group;
    }