anchor.diff:         ;; now actually layout the children
          (let ((x 0))
            (loop
  -             for child in (sheet-children pane)
  +             for child in (reverse (sheet-enabled-children pane))
                for major in majors
                for minor in minors
                do
  -               (let ()
  -                 #+NIL
  -                 (format T "~&;;   child ~S at 0, ~D ~D x ~D~%"
  -                         child x width height)
  -                 (move-sheet child
  -                             ((lambda (major minor) height width) x 0)
  -                             ((lambda (major minor) width height) x 0))
  -                 (allocate-space child
  -                                 width height)
  -                 )
  +               #+NIL (format T "~&;;   child ~S at 0, ~D ~D x ~D~%" child x width height)
  +               (move-sheet child
  +                           ((lambda (major minor) height width) x 0)
  +                           ((lambda (major minor) width height) x 0))
  +               (allocate-space child
  +                               width height)
                  (incf x major)
                  (incf x major-spacing)))))) )
  +
  +#+NIL
  +(defmethod note-sheet-enabled :before ((pane pane))
  +  ;; hmmm
  +  (when (panep (sheet-parent pane))
  +    (change-space-requirements pane)) )
  +
  +#+NIL
  +(defmethod note-sheet-disabled :before ((pane pane))
  +  ;; hmmm
  +  (when (panep (sheet-parent pane))
  +    (change-space-requirements pane)) )
   
   ;;;;
   
  
positive.code: 
   (defmethod box-layout-mixin/xically-allocate-space-aux* ((box box-layout-mixin) width height)
     (declare (ignorable width height))
     (let ((children (sheet-children box)))
       (with-slots (major-spacing) box
         (let* ((content-srs (mapcar #'(lambda (c) (xically-content-sr** box c)) children))
                (allot       (mapcar #'ceiling (mapcar #'space-requirement-major content-srs)))
  
negative.code: 
   (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)))
  
   (defclass xrack-pane (rack-layout-mixin xbox-pane)
     ()
  