//Typing a value outside the range clears the value when leaving the cell
FarPoint.Win.Spread.ValueProcess cnotify = new FarPoint.Win.Spread.ValueProcess();
cnotify.ValueProcessOption = FarPoint.Win.Spread.ValueProcessOption.Clear;
FarPoint.Win.Spread.TextLengthValidator tvalid = new FarPoint.Win.Spread.TextLengthValidator();
tvalid.LengthUnit = FarPoint.Win.Spread.LengthUnit.Char;
tvalid.MaximumLength = 6;
tvalid.MinimumLength = 0;
tvalid.Actions.Add(cnotify);
fpSpread1.Sheets[0].AddValidators(new FarPoint.Win.Spread.Model.CellRange(1, 1, 1, 1), tvalid);