两个信号处理器被连接起来——一个用来在用户关闭窗口时退出应用程序，另一个用来在用户点击按钮时，修改显示的欢迎信息。

Two signal handlers are connected — one to quit the application when the user closes the window and another to change the greeting that is displayed when the user clicks the button.

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Close——允许选项卡关闭(显示一个Close按钮)。

Close — Allows the TAB to close (shows a close button).

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显示/取消标签页的关闭按钮

Show/Disable Close button on Tabs

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