Sections X00, X10, X11, X30, X48, X50, X51, X55, X80, X81, X82, and X85 contain general information on the data elements defined for use in the 1XX (heading), 4XX (see from tracing), 5XX (see also from tracing), and 7XX (heading linking entry) fields. In MARC 21, the definitions of data elements in many fields are carried over to other fields within the same group (e.g., the 1XX fields) for consistency and as a mnemonic aid. This is particularly true of the fields defined for names, uniform titles, and terms used in headings or subdivisions to headings.
Each General Information section contains a list of content designators defined (fields, indicators, and subfield codes), guidelines for applying the content designators that are shared, and input conventions for the fields within the group. Content designators that are not valid for all fields in a group are generally not described fully in the general information sections, instead, reference is made to where a complete description can be found.
Examples given in a general information section usually represent a variety of field tags. For a larger number of field-specific examples, as well as field-specific definition and scope or guidelines for applying content designators, refer to one of the 1XX, 4XX, 5XX, or 7XX field sections.