第二种选择允许对已知扩展的JSON序列化进行优化和简化，但是仍然限制了序列化的效用。

The second choice allows the JSON serialization of known extensions to be optimized and simplified but still limits the usefulness of the serialization.

youdao

完全隐藏允许SSH访问的事实，要求根据特殊的“敲门”序列识别有效用户。

Completely hiding the fact that you even allow SSH access and requiring a special "knock" sequence to be recognized as a possible user.

youdao