This control creates a check box to display a choice between one of two possible options. When it is checked it holds a true value in the XML and it becomes empty string when it is unchecked. You need to set type of "Check" in the data model to use it when designing form.
Form Design Actions
Include Page Other Properties Other Properties
Design
Label
Label is a caption of the checkbox on the user interface.
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Unchecked Value
It represents an empty string value.Other Properties Include Page