anchor.diff:  (defgeneric text-style-family (text-style))
   (defgeneric text-style-face (text-style))
   (defgeneric text-style-size (text-style))
  -(defgeneric merge-text-style (text-style-1 text-style-2))
  +(defgeneric merge-text-styles (text-style-1 text-style-2))
   (defgeneric text-style-ascent (text-style medium))
   (defgeneric text-style-descent (text-style medium))
   (defgeneric text-style-height (text-style medium))
  
positive.code: 
  ;;; Text-style utilities
  
  (defun merge-text-styles (s1 s2)
    (if (and (not (device-font-text-style-p s1))
  	   (not (device-font-text-style-p s2)))
        (let ((new-style (make-text-style (or (text-style-family s1)
  
negative.code: 					(or (text-style-size s1)
  					    (text-style-size s2)))))
  	(with-slots (size) new-style
  	  (case (text-style-size s1)
  	    (:smaller
  	     (setq size (find-smaller-size (text-style-size s2))))
  	    (:larger
  