The Focus Highlight
Each widget can have a focus highlight indicating which widget currently has the input focus. This is a thin rectangle around each widget that is displayed in the highlight background color by default. When the widget gets the input focus, the highlight rectangle is displayed in an alternate color. The addition of the highlight adds a small amount of space outside the border described in the previous section. The attributes in Table 37-3 control the width and color of this rectangle. If the width is zero, no highlight is displayed.
By default, only the widgets that normally expect input focus have a nonzero width highlight border. This includes the text, entry, and listbox widgets. It also includes the button and menu widgets ...
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