This element should be present as a subelement of the fwd or rev element.
这个元素应该作为 fwd 元素或 rev 元素的子元素出现。
2
If a FWD element that contains one or more via elements is present, the receiver should remove and inspect the top via subelement of FWD and verify that it is the intended recipient of the message.
This receiver will become the ultimate destination when (1) there are no via elements listed in the FWD element after the removal of the top via element, and (2) there is no to element.