X53 Subfield: $a - Classification number element - Single number or beginning number of span

Subfield $a contains either an element of a single classification number or an element of the beginning number of a classification number span. The element may consist of the whole classification number or a part of the classification number. The division of a classification number into elements is determined by the scheme-specific conventions established for the classification scheme identified in field 084 (Classification Scheme and Edition) .