Using <C-,> causes "<80>ü^D," to flash in the showcmd area?

Question

I've mapped <C-,> as well as some other special keys (<C-Enter>, <C-S-Space>, ...) in my vimrc like,

:set  <F13>=^[[44;5u
:map  <F13> <C-,>
:map! <F13> <C-,>

and configured iTerm to send ^[[44;5u when <C-,> is typed.

(Note that ^[ is the ascii Escape character.)

It works great, but Vim flashes <80>ü^D, in the showcmd area whenever I use <C-,>. Here's a screenshot (see the bottom-right corner):

It doesn't inhibit the mapping or seem to cause any problems, I'm just curious what it indicates. None of my other special mappings (<C-Enter> and the like) do this.

Do you know?

Answer 1

<80>ü^D, is how Vim displays its four-byte internal representation of <C-,>:

First byte: <80>

This is how Vim displays the byte 0x80. This value is K_SPECIAL. It is the first byte of a "special" keycode, and it is always followed by two bytes.

Second byte: ü

This is how Vim displays the byte 0xFC (the Unicode character U+00FC is LATIN SMALL LETTER U WITH DIAERESIS).

0xFC (or 252 in decimal) is KS_MODIFIER, and it means that the third byte will be a bitmask specifying which modifier was pressed.

Third byte: ^D

This is how Vim displays CTRL-D, the byte 0x04. In this context, 0x04 is MOD_MASK_CTRL.

Bytes 1–3: <80>ü^D

So, putting these together, we see that <80>ü^D means <C-

Fourth byte: ,

This one is simpler to figure out. It means ,.

In combination

So the four bytes <80>ü^D, means <C-,>, which is what you entered (via the mapping), and Vim helpfully displays this in the 'showcmd' area, as you requested!