code: def is_date(property_name, *, format=None, present_optional=False, message=None):
      
      # NOTE: Not currently using format param
      def check(val):
        """Checks that a value can be parsed as a date."""
        if val is None:
          return present_optional
        else:
          is_date, _ = util.try_parse_date(val)
          return is_date
  
      return Validation(check, property_name, message)
docs: Returns a Validation that checks a value as a date.