anchor.diff:  
    (defmethod initialize-instance :after ((pane xbox-pane) &key contents &allow-other-keys)
      (let ((children (mapcar (lambda (content)
  -                   (cond ((panep content)
  -                          content)
  -                         ;;
  -                         ((or (eql content +fill+) (eql content '+fill+))
  -                          (let ((child (make-instance 'null-pane)))
  -                            (setf (constraint-slot pane child 'fill-p) t)
  -                            child))
  -                         ;;
  -                         ;; what about something like (30 :mm) ?
  -                         ;;
  -                         ((and (realp content) (>= content 0))
  -                          (let ((child (make-instance 'null-pane)))
  -                            (setf (constraint-slot pane child 'fixed-size) content)
  -                            child))
  -                         ;;
  -                         ;; match (<n> <pane>)
  -                         ;;
  -                         ((and (consp content)
  -                               (realp (car content))
  -                               (>= (car content) 0)
  -                               (consp (cdr content))
  -                               (panep (cadr content))
  -                               (null (cddr content)))
  -                          (let ((number (car content))
  -                                (child  (cadr content)))
  -                            (if (< number 1)
  -                                (setf (constraint-slot pane child 'proportion) number)
  -                                (setf (constraint-slot pane child 'fixed-size) number))
  -                            child))
  -                         (t
  -                          (error "~S is not a valid element in the ~S option of ~S."
  -                                 content :contents pane)) ))
  -                 contents)))
  -     (mapc (curry #'sheet-adopt-child pane) children)
  -     (reorder-sheets pane children)))
  +                             (cond ((panep content)
  +                                    content)
  +                                   ;;
  +                                   ((or (eql content +fill+) (eql content '+fill+))
  +                                    (let ((child (make-instance 'null-pane)))
  +                                      (setf (constraint-slot pane child 'fill-p) t)
  +                                      child))
  +                                   ;;
  +                                   ;; what about something like (30 :mm) ?
  +                                   ;;
  +                                   ((and (realp content) (>= content 0))
  +                                    (let ((child (make-instance 'null-pane)))
  +                                      (setf (constraint-slot pane child 'fixed-size) content)
  +                                      child))
  +                                   ;;
  +                                   ;; match (<n> <pane>)
  +                                   ;;
  +                                   ((and (consp content)
  +                                         (realp (car content))
  +                                         (>= (car content) 0)
  +                                         (consp (cdr content))
  +                                         (panep (cadr content))
  +                                         (null (cddr content)))
  +                                    (let ((number (car content))
  +                                          (child  (cadr content)))
  +                                      (if (< number 1)
  +                                          (setf (constraint-slot pane child 'proportion) number)
  +                                          (setf (constraint-slot pane child 'fixed-size) number))
  +                                      child))
  +                                   (t
  +                                    (error "~S is not a valid element in the ~S option of ~S."
  +                                           content :contents pane)) ))
  +                           contents)))
  +     (mapc (curry #'sheet-adopt-child pane) children)))
   
    (defclass xrack-pane (rack-layout-mixin xbox-pane)
      ()
  
positive.code:             (compose-space child)) )))
  
   (defmethod box-layout-mixin/xically-compose-space ((pane box-layout-mixin))
     (let ((n (length (sheet-children pane))))
       (with-slots (major-spacing) pane
         (loop
             for child in (sheet-children pane)
             for sr = (xically-content-sr** pane child)
             sum (space-requirement-major sr) into major
             sum (space-requirement-min-major sr) into min-major
  
negative.code: ;;   . DUIM's default for maxima is not +fill+ but the dimension
  ;;
  ;; - what are the appropriate default values for align?
  ;;
  
  ;; - for layout purposes the list of children should be considered in
  ;;   reverse: The first element of children should come last.
  
  ;;--GB 2002-02-27
  
  ;;; GENERIC FUNCTIONS
  