Each bibliographic record contains alphanumeric data. Tags are in sequence according to the first digit. However, they are not necessarily in numeric sequence within a block of tags beginning with the same number. Even though the nature of cataloging data is such that many tags are not repeated, most variable tags may be repeated. Each variable field ends with a field terminator. The last field ends with both a field terminator and a record terminator.
In OCLC-MARC Records, any element, value, field, subfield, etc., marked obsolete is no longer valid. Current records will not contain these invalid codes. However, records supplied from archives (e.g., OCLC Local Database Creation service records) may contain obsolete MARC coding.
Unless described otherwise, all fields are valid in all formats. See Bibliographic Formats and Standards for additional information.