;;; The caller can supply :ALLOW-OTHER-KEYS T to suppress checking.
 ((lambda (&key x) x) :x 1 :y 2 :allow-other-keys t) ⇒  1
;;; The callee can use &ALLOW-OTHER-KEYS to suppress checking.
 ((lambda (&key x &allow-other-keys) x) :x 1 :y 2) ⇒  1
;;; :ALLOW-OTHER-KEYS NIL is always permitted.
 ((lambda (&key) t) :allow-other-keys nil) ⇒  T
;;; As with other keyword arguments, only the left-most pair
;;; named :ALLOW-OTHER-KEYS has any effect.
 ((lambda (&key x) x) 
  :x 1 :y 2 :allow-other-keys t :allow-other-keys nil)
⇒  1
;;; Only the left-most pair named :ALLOW-OTHER-KEYS has any effect,
;;; so in safe code this signals a PROGRAM-ERROR (and might enter the
;;; debugger).  In unsafe code, the consequences are undefined.
 ((lambda (&key x) x)                   ;This call is not valid
  :x 1 :y 2 :allow-other-keys nil :allow-other-keys t)