PAN No validation in Ax 2009

Hi,
     In Employee Details we can customize a string field  called PAN No.for that field we need some validation.

1.EmplTable --> Add a new string Field named  PAN No.
2.Add this field in EmplTable form design.
3.In EmplTable  form DataSource -->PAN No-->Modified method .
4.write the following code in modified method

public void modified()
{
    EmplTable   _emplTable;

    ;

    #define.alphabets('ABCDEFGHIJKLMNOPQRSTUVWXYZ')
    #define.numbers('0123456789')
    #COSNumbers
    if (( EmplTable.PANNO )&&
   ((strkeep(substr(EmplTable.PANNO, #1, #5), #alphabets) != substr(EmplTable.PANNO, #1, #5))         ||
        (strkeep(substr(EmplTable.PANNO, #6, #4), #numbers)   != substr(EmplTable.PANNO, #6, #4))
        ||
        (strlen(EmplTable.PANNO) != #10)  
        ||
 (strkeep(substr(EmplTable.PANNO, #10, #1), #alphabets) != substr(EmplTable.PANNO, #10,#1))) )
    {

       Throw error("@GLS5849");
    }

    select _emplTable where _emplTable.PANNO == EmplTable.PANNO
                                       && _emplTable.EmplId != EmplTable.EmplId;
    if (_emplTable)
    {
        if(_emplTable.PANNO)
        Throw error("PAN Number already exists");
     }

    super();
}

 *****************
create following lable
@GLS5849 = The Permanent Account Number (PAN) must be alphanumeric with 5 alpha, 4 numeric, and 1 alpha characters.
******************