The ISSN from field 022 of the related record. International Standard Book No. The ISBN from field 020 of the related record. Materials specified Distinguishes a subset of the described materials. Determine placement according to use.
Control subfield The first subfield.
Not applicable Position 2. If position 1 is u or n, use code n in position 2. Use a Type code. Use a BLvl code. You must differentiate pre-AACR2 serials that have the same title proper, but no distinguishing uniform title.