These are used to indicate a target element in the out going message assembly, where an acquired value should overwrite the existing value (in the case where the element already exists in the tree).

这些表达式用于指示输出消息组件中的目标元素，其中获取的元素应该重写现有值(假如树中已经存在元素)。

youdao

In the case where the described target element already exists in the out going message assembly, then the element is left untouched.

如果描述的目标元素已经存在于输出消息组件中，那么该元素保持不变。

youdao

"So in all of that, let's not have a message going out that patient safety was compromised - it wasn't, " Mr Poots added.

BBC: Ulster Hospital

And right before the ball dropped, he said, I'm going to say a message to fans: You guys out there - those players out there are working their butts off - and you sit there and boo them.

NPR: In the Era of Sports Scandal, Pity the Fan