27.1.1 Requirements for removed and deprecated features

For this standard, some features from the language described in Common Lisp: The Language have been removed, and others have been deprecated (and will most likely not appear in future Common Lisp standards). Which features were removed and which were deprecated was decided on a case-by-case basis by the X3J13 committee.

Conforming implementations that wish to retain any removed features for compatibility must assure that such compatibility does not interfere with the correct function of conforming programs. For example, symbols corresponding to the names of removed functions may not appear in the the COMMON-LISP package. (Note, however, that this specification has been devised in such a way that there can be a package named LISP which can contain such symbols.)

Conforming implementations must implement all deprecated features. For a list of deprecated features, see Deprecated Language Features.