Information concerning the host item for the constituent unit described in the record (vertical relationship). In the case of host items that are serial or multi-volume in nature, information in subfields $g and $q is necessary to point to the exact location of the component part within the bibliographic item.
When a note is generated from this field, the introductory term In may be generated based on the field tag for display.
Provided in order to enable the user to locate the physical piece that contains the component part or subunit being described. Thus, only those data elements required to assist in the identification of the host item need to be included in the field, such as links to the bibliographic record describing the item and/or descriptive data that identify the host item.