Extending Microsoft Dynamics 365 Business Central Tables via AL Language

tableextension 50100 "CustomerMpesaExt" extends Customer
{
    fields
    {
        field(50100; "M-Pesa Mobile Number"; Text[20])
        {
            Caption = 'M-Pesa Mobile Number';
            DataClassification = CustomerContent;

            trigger OnValidate()
            var
                Regex: Codeunit Regex;
            begin
                if "M-Pesa Mobile Number" <> '' then begin
                    "M-Pesa Mobile Number" := DelChr("M-Pesa Mobile Number", '=', ' -+');
                    if not Regex.IsMatch("M-Pesa Mobile Number", '^254[0-9]{9}$') then
                        Error('Invalid Kenyan phone number format.');
                end;
            end;
        }
    }
}