//Typing a value outside the range prevents focus from leaving the cell
FarPoint.Win.Spread.FocusProcess cnotify = new FarPoint.Win.Spread.FocusProcess();
cnotify.PreventFocusLeave = true;
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);