dbg:*hidden-packages*
is used by the debugger. It should be bound to a list of package specifiers. If a package is included in the list then any symbols in it are not shown by the debugger. Thus during backtraces the call frames corresponding to functions in these packages are not displayed. This can be useful in restricting the debugger to particular areas.
CL-USER 1 > unbound
Error: The variable UNBOUND is unbound.
1 (continue) Try evaluating UNBOUND again.
2 Return the value of :UNBOUND instead.
3 Specify a value to use this time instead of evaluating UNBOUND.
4 Specify a value to set UNBOUND to.
5 (abort) Return to level 0.
6 Return to top loop level 0.
Type :b for backtrace or :c <option number> to proceed.
Type :bug-form "<subject>" for a bug report template or :? for other options.
CL-USER 2 : 1 > :b 3
Call to ERROR
Call to EVAL
Call to CAPI::CAPI-TOP-LEVEL-FUNCTION
CL-USER 3 : 1 > (push "COMMON-LISP" dbg:*hidden-packages*)
("COMMON-LISP" #<The COMPILER package, 3131/4096 internal, 41/64 external> #<The SYSTEM package, 6258/8192 internal, 1266/2048 external> "DBG" "CONDITIONS")
CL-USER 4 : 1 > :b 3
Call to CAPI::CAPI-TOP-LEVEL-FUNCTION
Call to CAPI::INTERACTIVE-PANE-TOP-LOOP
Call to MP::PROCESS-SG-FUNCTION
CL-USER 5 : 1 >