The Library of Congress Classification schedules have traditionally used parentheses around certain class numbers to indicate one of two conditions: (1) the number was formerly valid but is now obsolete and no longer used by LC, or (2) the number is an optional number that was never used by LC but is provided for those libraries that wish to follow an arrangement that differs from LC practice. In either case, a see reference or explanatory note generally appears at the location of the parenthesized number to indicate to the user the valid number currently used by LC.
The Library has introduced a change in the display conventions for these two types of numbers. Numbers of the first type continue to be displayed in parentheses, but numbers of the second type are now displayed in angle brackets. See references or explanatory notes continue to appear under both types of numbers. This change in displays has already been implemented in Classification Web, the Library's online Web-based classification product. Angle brackets will also appear in new printed editions of the classification schedules dated 2003 or later.
Examples of numbers that were formerly parenthesized but now appear in angle brackets are at JZ5528 , KF175, and PS8001-8599.