anchor.diff:  (defstruct editor-variable
     value
     documentation
  -  local-indicator)
  +  local-indicator
  +  change-value-hook)
   
   (defun clear-editor-local-variables (buffer)
     (dolist (symbol *editor-variables*)
  
positive.code:      (setf (get ',var 'editor-variable)
             (make-editor-variable :value ,value
                                   :documentation ,documentation
                                   :local-indicator (gensym ,(string var))))
       t))
  
  (defun editor-variable-error (symbol)
  
negative.code:                              (editor-variable-local-indicator var))
                 value)))
        ((:global)
         (let ((fn (editor-variable-change-value-hook var)))
           (when fn
             (funcall fn value)))
         (setf (editor-variable-value var) value)))))
  
  (defun variable-documentation (symbol)
  