Variable 1 default = OCLC: The OCLC number that can be found in the permalink in the item's record as found in BSB's online catalog. Using the OCLC is not recommended as BSB changed their permalinks, and this is only for backwards compatibility.
Variable 2 can be used with U in the first field for the urn - the number found at the end of the string urn:nbn:de:bvb:### {{BSB|U|###}}
Variable 2 can also be used with D in the first field for the digital object id {{BSB|D|digital object id}}
