If non-nil, keep cross-reference information that is used by functions like hcl:who-calls and hcl:calls-who.
Compatibility note: In LispWorks 6.1 and earlier versions cross-reference information is kept if any of the functions that use it is kept. Now the cross-reference information is cleared even if any of these functions is kept, unless this keyword is non-nil.
LispWorks Delivery User Guide - 10 Aug 2017