这两个函数均按照深度优先的顺序遍历树，但两者的差异在于先访问一个节点还是先访问其子节点。
Both functions walk the tree in depth-first order but they differ in whether a node is visited before or after its children.
消息流编辑器现在可以记住访问特定节点时的最后一个制表位。
The Message Flow Editor will now remember the last TAB that you visited for a particular node.
图4展示了一个更类似的场景——事务中的第二个查询需要访问与第一个查询相同的节点上的数据。
Figure 4 shows a more likely scenario — that the second query in the transaction needs to access data on the same node as the first query.
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