Here, we have only one operation and interface, so you can define the qualifier at any level.
我们此处仅有一个操作和一个接口，因此可以在任何级别定义限定符。
In DOM Level 2, renaming a node was a relatively expensive operation: You had to create a new node, copy all the data to the new node, insert the new node into the tree, and delete the old one.
在DOM Level 2中，重命名一个节点的操作代价较高：必须在树中创建一个新节点，并删除老的节点。
An operation at a high level requires the execution of one or more operations at lower levels.
一个高层次上的操作需要执行一个或多个更低层次上的操作。
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