anchor.diff:      (force-output stream)
       ;; Why is this binding here? We need the "environment" in this call that
       ;; computes the new records of an outer updating output record to resemble
  -    ;; that when a record's contents are computed in invoke-updating-output. 
  +    ;; that when a record's contents are computed in invoke-updating-output.
       (letf (((stream-current-output-record stream)
   	    (output-record-parent record)))
  -      (compute-new-output-records-1 record 
  +      (compute-new-output-records-1 record
   				    stream
   				    (output-record-displayer record)))))
   
  
positive.code:                         (pane-viewport-region (updating-output-stream record))))
          (was-table (make-hash-table :test #'equalp))
          (is-table (make-hash-table :test #'equalp)))
      
      (labels ((collect-1-was (record)
                 (push record was)
                 (push record (gethash (output-record-hash record) was-table)))
  
negative.code: closures  the child updating output records are called because any free
  variables captured in the UPDATING-OUTPUT forms need to see the fresh bindings
  from this run of the code.As UPDATING-OUTPUT forms are encountered, several
  things can happen:
  
  * The cache value of the form compares to the value stored in the record.  The
  record, and all the updating output records below it, are marked :clean.  The
  