A subject heading is assigned to a substantial portion of a work (at least 20%) covering a distinctive subject which is not adequately represented by the heading(s) assigned to the entire work. An additional heading representing a specific example used to illustrate the principle which is the main focus of the work may also be assigned, provided the example occupies at least 20% of the work.

21.2 References

See also:

21.0 Depth (levels) of subject cataloging