Subfield $2,
Source of heading or term, has been added to a number of heading fields
1); this subfield contains a code that identifies the source from which the heading was assigned. Support for this new role has been added to the context-sensitive code lists that appear when pressing F7 in MARC Report while editing a record. (To demonstrate this, go to the end of a 1XX field, type ±2, then press F7).