How to allow a user to select only dates that are weekdays on Nintex Forms

1.To allow a user to select only dates that are weekdays (i.e. Monday-Friday) you can use a data validation rule with a custom formula using FormatDate Inline function.
Usage:
formatDate(date, format) or formateDate({namedControl}, "D")
2.Create a Date/time control
3.Add the following validation rule to the the date/time control 

or(equals(formatDate({Self},"dddd"),"Saturday"),equals(formatDate({Self},"dddd"),"Sunday"))

"dddd" will format the date as the day's name, "Sunday" for example.