090, 852 are all common in MARC21) and the subfield codes without the
delimiters ($a, $b would be ab).
+- If you want several fields to be the source of the item's call number,
+ simply separate the fields with 'or'. See examples below.
+
Examples:
- Dewey: 082ab or 092ab; LOC: 050ab or 090ab; from the item record: