863-865 $w - Break indicator:
Subfield $w contains a one-character code that indicates whether a break in the enumeration and chronology contained in multiple 863-865 fields is due wither to published issue(s) lacking in the collection or to unpublished parts or a lack of continuity in the enumeration and chronology of the parts. Subfield $w is contained in the Enumeration and Chronology field that represents the holdings that immediately precedes the break. The use of subfield $w requires a new field 863-865 in which the enumeration and chronology following the break is recorded.