>Nadya,
>
>A is a template character as is 9. A allows any character and 9 any digit. I would try doing this using a label and textbox. The label shows AO and the textbox allows entry of the other characters. You can use the Valid event to replace the field with the "AO" + textbox.Value and the Refresh to display the SUBSTR(FieldName,3).

Hi Jim,

I implemented my own solution based on GotFocus(), but just discovered, that it's not working 100% reliably. I think, I'll give your idea a go then.

Thanks a lot.