如果可以在一个subscriptions表中收集那些对通知的请求，就很容易实现这一点。
That could easily be achieved if you could collect such requests for notification in a SUBSCRIPTIONS table.
该消息的实际显示方式是特定于实现的；目前，GNOME通知区显示工具提示。
How this message is actually displayed is implementation specific; at present the GNOME notification area displays a tooltip.
要接收通知，高级回调接口的实现必须要用MQTT客户端注册。
To receive notifications, an implementation of the advanced callback interface must be registered with the MQTT client.
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