By default, AllowEmptyValue property is exNoEmptyValue. The AllowEmptyValue property indicates whether the field supports empty values. This option can be used with invalid flag, which indicates that the user can leave the field if it is empty. If empty flag is present, the field displays nothing if no entity is completed ( empty ). Once the user starts typing characters the current mask is displayed. For instance, having the mask "!(999) 000 0000;;;empty,select=4,overtype,invalid=invalid phone number,beep", it specifies an empty or valid phone to be entered.