To avoid a server round trip, the format mask of a date picker item/column should automatically be checked in the browser when the value gets changed. If the date validation fails, the user shouldn't be allowed to leave the item/column.
The following additional features should be supported.
-) If the format mask uses YYYY, RR should also be supported => expand the value to 4 digits.
-) If the user enters =, -x or +x (eg -1 for yesterday), it should be expanded to the current date + x