A citation for a consulted source in which information is found about the 1XX
heading in an established heading record. The information found in the source may also be present.
Each additional source of information is recorded in a separate 933 note.
$a - Source citation (NR). In UNBIS, the entire note is recorded in subfield $a.
933 $a Macrothésaurus
933 $a Thésaurus de l'Unesco
933 $a http://www.unicode.org/unicode/standard/WhatIsUnicode.html
933 $a Dictionnaire futunien-français ..., 1993