anchor.diff:  (defgeneric adjust-item-list-cells (item-list-record stream))
   
   (defclass standard-item-list-output-record (item-list-output-record
  -                                            block-output-record-mixn
  +                                            block-output-record-mixin
                                               standard-sequence-output-record)
     ((x-spacing :initarg :x-spacing)
      (y-spacing :initarg :y-spacing)
  
positive.code: 
  ;;; Generic block formatting
  (defclass block-output-record-mixn ()
    ()
    (:documentation "The class representing one-dimensional blocks of cells."))
  
  (defmethod replay-output-record ((bl block-output-record-mixn) stream
                                   &optional region (x-offset 0) (y-offset 0))
    (when (null region)
      (setq region (or (pane-viewport-region stream) +everywhere+)))
  
negative.code: 
  ;;; STANDARD-COLUMN-OUTPUT-RECORD class
  (defclass standard-column-output-record (column-output-record
                                           block-output-record-mixin
                                           standard-sequence-output-record)
    ())
  
  