anchor.diff:  					     ;:pointer-motion
                                                 :button-motion)))
     (when (null (port-lookup-mirror port sheet))
  +    (update-mirror-geometry sheet)
       (let* ((desired-color (typecase sheet
                               (sheet-with-medium-mixin
                                 (medium-background sheet))
  
positive.code: #+NIL
  (defmethod (setf sheet-mirror-transformation) :after (new-value (sheet mirrored-sheet-mixin))
    )
  
  (defun invent-sheet-mirror-transformation-and-region (sheet)
    ;; -> tr region
  
negative.code:            (color (multiple-value-bind (r g b)
                        (color-rgb desired-color)
                      (xlib:make-color :red r :green g :blue b)))
             (pixel (xlib:alloc-color (xlib:screen-default-colormap (clx-port-screen port)) color))
             (window (xlib:create-window
                      :parent (sheet-mirror (sheet-parent sheet))
                      :width (if (%sheet-mirror-region sheet)
                                 (round-coordinate (bounding-rectangle-width (%sheet-mirror-region sheet)))
                                 width)
                      :height (if (%sheet-mirror-region sheet)
                                 (round-coordinate (bounding-rectangle-height (%sheet-mirror-region sheet)))
                                 height)
                      :x (if (%sheet-mirror-transformation sheet)
                                 (round-coordinate (nth-value 0 (transform-position
                                                                 (%sheet-mirror-transformation sheet)
                                                                 0 0)))
                                 x)
                      :y (if (%sheet-mirror-transformation sheet)
                             (round-coordinate (nth-value 1 (transform-position
                                                             (%sheet-mirror-transformation sheet)
                                                             0 0)))
                             y)
                      :border-width 0 ;;border-width
                      :border border
                      :override-redirect override-redirect
                      :backing-store backing-store
  