The special value of `unspecified' means to check whether \"ls\"
supports the \"--dired\" option, and save the result in this
variable. This is performed the first time `dired-insert-directory'
-is invoked.
+is invoked. (If `ls-lisp' is used by default, the test is performed
+only if `ls-lisp-use-insert-directory-program' is non-nil, i.e., if
+Dired actually uses \"ls\".)
Note that if you set this option to nil, either through choice or
because your \"ls\" program does not support \"--dired\", Dired