+In particular, it is important to realize that dynamic extend is
+contagious:
+
+@lisp
+(let* ((a (list 1 2 3))
+ (b (cons a a)))
+ (declare (dynamic-extent b))
+ ;; Unless A is accessed elsewhere as well, SBCL will consider
+ ;; it to be otherwise inaccessible -- it can only be accessed
+ ;; through B, after all -- and stack allocate it as well.
+ ;;
+ ;; Hence returning (CAR B) here is unsafe.
+ ...)
+@end lisp
+
+This allows stack allocation of complex structures. As a notable
+exception to this, SBCL does not as of 1.0.48.21 propagate
+dynamic-extentness through @code{&rest} arguments -- but another
+conforming implementation might, so portable code should not rely on
+this.
+
+@lisp
+(declaim (inline foo))
+(defun foo (fun &rest arguments)
+ (declare (dynamic-extent arguments))
+ (apply fun arguments))
+
+(defun bar (a)
+ ;; SBCL will heap allocate the result of (LIST A), and stack allocate
+ ;; only the spine of the &rest list -- so this is safe, but unportable.
+ ;;
+ ;; Another implementation, including earlier versions of SBCL might consider
+ ;; (LIST A) to be otherwise inaccessible and stack-allocate it as well!
+ (foo #'car (list a)))
+@end lisp