Common Lisp the Language, 2nd Edition
Methods for update-instance-for-redefined-class may be defined
to specify actions to be taken when an instance is updated. If only
:after methods for update-instance-for-redefined-class are
defined, they will be run after the system-supplied primary method for
initialization and therefore will not interfere with the default
behavior of update-instance-for-redefined-class. Because no
initialization arguments are passed to
update-instance-for-redefined-class when it is called by the system,
the :initform forms for slots that are filled by :before
methods for update-instance-for-redefined-class will not be
evaluated by shared-initialize.
Methods for shared-initialize may be defined to customize class
redefinition (see section 28.1.9.5).
