Check boxes detected within forms (Textract selectables as key-value pairs) are supported. In this case, you can choose to map to d:boolean (i.e. whether selected or not) or d:text. For d:text, the selected status value is stored as returned by Textract, i.e. SELECTED or NOT_SELECTED.
Here's an example of the metadata extracted from a form that shows both options mixed together in a single aspect: