LispWorks detects attempts to define external symbols in the packages on the list
*packages-for-warn-on-redefinition*
.
LispWorks, as distributed, is configured to protect the COMMON-LISP package and other system packages.
In particular, the effect of including
"COMMON-LISP"
in the list value of
*packages-for-warn-on-redefinition*
is to make all COMMON-LISP symbols be reserved words in respect of definitions and bindings. LispWorks is configured like this because ANSI Common Lisp states that the consequences of such definitions and bindings are undefined. Therefore they are best avoided.
The action taken by LispWorks on such attempted definitions depends on the value of *handle-warn-on-redefinition*.