-;;; Check to see whether OBJECT is a circular reference, and return something
-;;; non-NIL if it is. If ASSIGN is T, then the number to use in the #n= and
-;;; #n# noise is assigned at this time. Note: CHECK-FOR-CIRCULARITY must
-;;; be called *EXACTLY* once with ASSIGN T, or the circularity detection noise
-;;; will get confused about when to use #n= and when to use #n#. If this
-;;; returns non-NIL when ASSIGN is T, then you must call HANDLE-CIRCULARITY
-;;; on it. If you are not using this inside a WITH-CIRCULARITY-DETECTION,
-;;; then you have to be prepared to handle a return value of :INITIATE which
-;;; means it needs to initiate the circularity detection noise. See the
-;;; source for info on how to do that.
+;;; Check to see whether OBJECT is a circular reference, and return
+;;; something non-NIL if it is. If ASSIGN is T, then the number to use
+;;; in the #n= and #n# noise is assigned at this time.
+;;; If ASSIGN is true, reference bookkeeping will only be done for
+;;; existing entries, no new references will be recorded!
+;;;
+;;; Note: CHECK-FOR-CIRCULARITY must be called *exactly* once with
+;;; ASSIGN true, or the circularity detection noise will get confused
+;;; about when to use #n= and when to use #n#. If this returns non-NIL
+;;; when ASSIGN is true, then you must call HANDLE-CIRCULARITY on it.
+;;; If CHECK-FOR-CIRCULARITY returns :INITIATE as the second value,
+;;; you need to initiate the circularity detection noise, e.g. bind
+;;; *CIRCULARITY-HASH-TABLE* and *CIRCULARITY-COUNTER* to suitable values
+;;; (see #'OUTPUT-OBJECT for an example).