When the library has enabled xpath in record.abs (zebra mode), then the librarian can enter a PQF to query a given MARC subfield.
In Koha 2.2 the possibility to query any MARC subfield was enjoyed by librarians. It can be reintroduced in v3.2, through a specific screen to choose the subfield to query & build the query. The result will be a direct PQF query.
Note : script already written by BibLibre (not added to 3.0)