anchor.diff:      `(progn
          (let ((,parent (stream-current-output-record ,stream)))
            (assert (or (row-output-record-p ,parent)
  -                     (column-output-record-p ,parent))))
  +                     (column-output-record-p ,parent)
  +                     (item-list-output-record-p ,parent))))
          (with-new-output-record (,stream ,record-type ,record
                                   :align-x ,align-x :align-y ,align-y
                                   :min-width (parse-space ,stream
  
positive.code: (defmethod map-over-column-cells
      (function (column-record standard-column-output-record))
    (map-over-output-records
     #'(lambda (record)
         (when (cell-output-record-p record) (funcall function record)))
     column-record))
  
  (defmacro formatting-column ((&optional (stream t)
  
negative.code: ;;; TODO:
  ;;;
  ;;; - Check types: RATIONAL, COORDINATE, REAL?
  ;;; - Check default values of unsupplied arguments.
  ;;; - Better error detection.
  ;;; - 
  ;;; - Multiple columns:
  ;;; - - all columns are assumed to have the same width;
  ;;; - - all columns have the same number of rows; they should have the
  