Repeatability of fields and subfields:

The MARC guidelines for each field and subfield indicate whether a field can be repeated within the same record or a subfield repeated within the same field.

Theoretically, all fields and subfields may be repeated.  The nature of the data in a field, however, often precludes repetition.  The repeatability or nonrepeatability of each field and subfield is specified.

Field and subfield repeatability/nonrepeatability is sometimes indicated in written and on-line MARC documentation by the abbreviations R or NR following the description of each field and subfield in the appropriate MARC format.

See also:

Field and Subfield Repeatability