Lisp lists are popular data structures in the C code as well as in
Elisp. There are two sets of macros that iterate over lists.
`EXTERNAL_LIST_LOOP_N' should be used when the list has been supplied
-by the user, and cannot be trusted to be acyclic and nil-terminated. A
-`malformed-list' or `circular-list' error will be generated if the list
-being iterated over is not entirely kosher. `LIST_LOOP_N', on the
+by the user, and cannot be trusted to be acyclic and `nil'-terminated.
+A `malformed-list' or `circular-list' error will be generated if the
+list being iterated over is not entirely kosher. `LIST_LOOP_N', on the
other hand, is faster and less safe, and can be used only on trusted
lists.