anchor.diff:  
    (defmethod initialize-instance :after ((pane xbox-pane) &key contents &allow-other-keys)
      (let ((children (mapcar (lambda (content)
  +                             ;; Note: if you extend the allowed
  +                             ;; "syntax" also update the XICALLY macro
  +                             ;; also. --GB
                                (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))
  +                                   ;;
  +                                   ((and (consp content)
  +                                         (or (member (car content) '(+fill+ :fill))
  +                                             (eql (car content) +fill+)))
  +                                    (let ((child  (cadr content)))
                                         (setf (constraint-slot pane child 'fill-p) t)
                                         child))
                                      ;;
  
positive.code: ;;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  ;;; Boston, MA  02111-1307  USA.
  
  ;;; $Id: panes.lisp,v 1.93 2002-07-31 11:58:10 adejneka Exp $
  
  (in-package :CLIM-INTERNALS)
  
  
negative.code:                ,@options
                 :contents (list ,@(mapcar (lambda (content)
                                             (cond ((and (consp content)
                                                         (or (realp (first content))
                                                             (member (first content) '(+fill+ :fill))))
                                                    `(list ',(first content)
                                                           ,(second content)))
                                                   (t
  