By design, the ComboBox widget is intended to allow custom values. In case you need to always limit the user to choose among the predefined values in the list, I would suggest you to use the DropDownList widget instead. The workaround demonstrated in the how-to article in question would allow the developer to alter the core functionality of the ComboBox widget. Nevertheless, I am afraid that such an option would not be appropriate to be available in the built-in functionality of the widget.
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