increment-register
increment-register is an interactive compiled Lisp function in `register.el
'.
It is bound to C-x r +.
(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.
Interactively, reads the register using `register-read-with-preview'.