The API documentation is only urging caution because by setting cleanstart to true, the broker is being asked to violate the contract for assured delivery of QoS 1 and 2 messages.

API文档只是提醒要多加小心，因为当将cleanstart设置为true时，就要求代理违反确保QoS 1和2消息传递的约定。

youdao

For sometime past we have been urging you for a punctual delivery.

曾几何时，我方一直催问你方准时交货。

youdao

There is a bipartisan call urging the President to expedite delivery of U.S. humanitarian assistance to the Syrian people, including the Syrian Opposition Council, coming from senators Ayotte and Kirsten Gillibrand.

WHITEHOUSE: Press Briefing

With the fervor of a convert, he's urging utilities across the country to build data-delivery systems on their power grids.

FORBES: Tilting at Power Lines