-(defun increment-register (number register)
- "Add NUMBER to the contents of register REGISTER.
-Interactively, NUMBER is the prefix arg."
- (interactive "p\ncIncrement register: ")
- (or (numberp (get-register register))
- (error "Register does not contain a number"))
- (set-register register (+ number (get-register register))))
+(defun increment-register (prefix register)
+ "Augment contents of REGISTER.
+Interactively, PREFIX is in raw form.
+
+If REGISTER contains a number, add `prefix-numeric-value' of
+PREFIX to it.
+
+If REGISTER is empty or if it contains text, call
+`append-to-register' with `delete-flag' set to PREFIX."
+ (interactive "P\ncIncrement register: ")
+ (let ((register-val (get-register register)))
+ (cond
+ ((numberp register-val)
+ (let ((number (prefix-numeric-value prefix)))
+ (set-register register (+ number register-val))))
+ ((or (not register-val) (stringp register-val))
+ (append-to-register register (region-beginning) (region-end) prefix))
+ (t (error "Register does not contain a number or text")))))