(progn
  (unless standard-display-table
    (setq standard-display-table (make-display-table)))
  (aset standard-display-table ?X
	(vector (make-glyph-code ?X 'shadow)))
  (aset standard-display-table ?Y
	(vector (make-glyph-code ?Y 'underline)))
  (aset standard-display-table ?Z
	(vector (make-glyph-code ?Z 'escape-glyph))))