Controls whether invisible frames are printed in debugger output.
This variable is used by the debugger when it displays the stack frames.
Invisible frames are those for functions with
hcl:invisible-frame declarations. These are normally not shown by the debugger. However if
*print-invisible-frames* is true then these frames are displayed.
*print-invisible-frames* can be set to value by
(set-debugger-options :invisible value
*print-invisible-frames* is an extension to Common Lisp.
LispWorks User Guide and Reference Manual - 20 Sep 2017