The source code for the tree controls shown in Figure 3 appears in Listing 4.

图3所示树控件的源代码见清单4。

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The check box before each node in the tree controls the enabling state of the element.

树中每个节点前的复选框控制元素的启用状态。

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Previously, tree controls were created out of lists and links so the user had to TAB to each tree item.

以前树形控件是通过清单和链接创建的，因此用户必须使用制表键跳到每个树项目。

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Wars since 1979 have ended all controls, while greatly increasing the number of poor people desperate to fell any tree they can find.

ECONOMIST: Missing trees reflect the country's woeful recent history