(or (delivery-value :keep-debug-mode)
(< *delivery-level* 5))
If the value is nil, the functions and values used to read Lisp expressions are deleted. This means that the listener no longer works. On non-Windows platforms it also prevents lw:user-preference and capi:top-level-interface-geometry-key from working.
The :keep-lisp-reader keyword is set to t automatically if :keep-debug-mode is t.
LispWorks Delivery User Guide - 10 Aug 2017