Is used for callnumber computation.
User must supply a letter prefix (unspecified length) followed by an empty space followed by a "number". "Number" is 4 character long, and is either a number sequence which is 01 padded. If input does not conform with this format any processing is omitted.
Some examples of legal values that trigger auto allocation:
AAA 0 - returns first unused number AAA 0xxx starting with AAA 0001 BBB 12 - returns first unused number BBB 12xx starting with BBB 1201 CCC QW - returns first unused number CCC QWxx starting with CCC QW01