protected function getGroupContents(): array
    {
        $contents = [];

        foreach ($this->children() as $key => $child) {

            if (is_string($child)) {
                $contents[] = [ 'key' => $child, 'type' => 'field' ];
                continue;
            }

            $contents[] = [ 'key' => $key, 'type' => $child->type() ];
        }

        return $contents;
    }