The key to retaining the MARC structure, while simultaneously reducing required coding specificity, is the fill character.  For MARC 21 records, the use of this fill character is limited to variable control fields such as field 008 (Fixed-Length Data Elements).  It may not be used in the leader or in tags, indicators, or subfield codes.  Presence of a fill character in a variable control field indicates that the creator of the record has not attempted to supply a value.  In contrast, use of a character signifying "unknown" in a variable control field indicates that the creator of the record has attempted to supply a value, but was unable to determine what the appropriate value should be.  The fill character may be used in undefined character positions and in character positions for which the MARC 21 format defines one or more values.  Use of the fill character in variable control fields is usually regulated by the policy of the inputting agency.

For communication purposes, the fill character is represented by the code point 7C(hex).  The fill character is represented graphically as the vertical bar ( | ).

NOTE:  Another use of 7C(hex) is as a placeholder for a character outside the MARC-8 repertoire in a record converted from Unicode to MARC-8.  This lossy conversion technique is described in Part 4.  There is no conflict between the functions of 7C(hex).  The places mentioned above where the 7C(hex) fill character is valid are constrained to use only characters in the ASCII repertoire; hence the placeholder 7C(hex) can only occur elsewhere, in the text of variable data fields.

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Part 1:  General Character Set Issues

Character Sets and Encoding Options