Hooking Business Logic with AL Event Subscribers

codeunit 50100 "Loyalty Events"
{
    [EventSubscriber(ObjectType::Table, Database::"Sales Header",
        'OnAfterValidateEvent', 'Sell-to Customer No.', true, true)]
    local procedure OnValidateCustomer(var Rec: Record "Sales Header")
    var
        Cust: Record Customer;
    begin
        if Cust.Get(Rec."Sell-to Customer No.") then
            if Cust."Loyalty Points" > 1000 then
                Message('VIP customer: apply loyalty discount.');
    end;
}