Verifying a field by having the user enter data twice

You can fail the validation on one or both of the fields is the user's input does not match. For example, override the second account number field's validate event and enter something like this

if(!firstaccountNumber.isNull && !this.isNull && firstaccountNumber.rawValue != this.rawValue){
false;
}

This will cause the second field to fail its validations if both fields are filled in and the contents do not match.