anchor.diff:       &key pointer multiple-window transformp (context-type t)
        (highlight nil highlight-p))
     ;; (setq pointer (port-pointer (port sheet))) ; FIXME
  -  (let ((port (port sheet))
  +  (let ((port (port sheet))        
           (presentations-p (or presentation-handler
                                presentation-button-press-handler
                                presentation-button-release-handler)))
  
positive.code:                                    ;; XXX specialize on EVENT?
                                     ;; :SUPER-AROUND?
                                     (queue-event sheet event))
        (with-input-context (context-type :override t) ()
          (loop for event = (event-read sheet)
             do (cond ((and (typep event 'pointer-event)
                            #+nil
                            (eq (pointer-event-pointer event)
                                pointer))
                       (let* ((x (pointer-event-x event))
                              (y (pointer-event-y event))
                              (window (event-sheet event))
  
negative.code:                                                 sheet ; XXX
                                                  x y
                                                  :modifier-state (event-modifier-state event)))))
                         (when (and highlight presentation)
                           (frame-highlight-at-position (pane-frame sheet) window x y))
                         ;; FIXME Convert X,Y to SHEET coordinates; user
                         ;; coordinates
                         (typecase event
  