*packages-for-warn-on-redefinition* is a list of package names or the keyword
:implementation, specifying packages which are "protected". For "protected" packages, LispWorks checks before defining (using any of the definer macros like
cl:defclass and so on) any external symbol of these packages, and takes the action specified by *handle-warn-on-redefinition* (which defaults to signaling an error).
*packages-for-warn-on-redefinition* indicates all of the packages which are part of the LispWorks implementation. That includes all the documented packages, including COMMON-LISP and KEYWORD but excluding some "user" packages like CL-USER and KW-USER, and some packages that are used internally.
:implementationfrom the list. In situations when this is required, you should do it by rebinding
*packages-for-warn-on-redefinition*rather than setting it.
cl:streamas a function gives an error (by default), even though
cl:streamhas only a class definition, and trying to define
cl:caras a class also errors even though
cl:carhas only a function definition.
LispWorks User Guide and Reference Manual - 20 Sep 2017