Currently the system preference "automembernum" only allows for the patron's barcode to default the card number field on the patron addition screen to the next available card number (for example, if the largest currently used card number is 26345000012941, then this field will default to 26345000012942). It would be nice for the library to choose the format of the barcode (for example : system preference autobarcode). Then a library could choose to include letters and numbers to their patron's barcode instead of just numbers.
Added a see also to a bug I filed about allowed manual definition of automembernum's values