因为只有文档节点和元素才能作为其他节点的父节点，因此筛选过后仅留下了文档节点。

Only document nodes and elements can be parents of other nodes, so that filter leaves only document nodes.

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在键入过程中，列表会自动筛选，仅显示匹配的元素。

As you type, the list filters itself to display only the matching elements.

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这些源模型和目标模型会得到筛选；只有那些选中元素的父类和所有子类才可以看见。

The source and target models are filtered; only the parents and all children of the selected element are visible.

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