Is there a calendar format that allows me to select a period rather than just a single day?
Example: 01/15/2026 - 02/20/2026
No, there is no ‘interval’ or equivalent data type in XForms/XLSForms. Instead, you will need to capture two distinct start and end dates (or datetimes, or times…). I would also recommend adding an explicit constraint that the end date must be after the start date.
