I would like to edit the file f2 in boot.img and perhaps add more help files.
The syslinux documentation says:

"DISPLAY and function-key help files are text files in either DOS or UNIX format (with or without <CR>). In addition, the following special codes are interpreted:

<FF> <FF> = <Ctrl-L> = ASCII 12
Clear the screen, home the cursor. Note that the screen is filled with the current display color.

<SI><bg><fg> <SI> = <Ctrl-O> = ASCII 15
Set the display colors to the specified background and
foreground colors, where <bg> and <fg> are hex digits,
corresponding to the standard PC display attributes:

0 = black 8 = dark grey
1 = dark blue 9 = bright blue
2 = dark green a = bright green
3 = dark cyan b = bright cyan
4 = dark red c = bright red
5 = dark purple d = bright purple
6 = brown e = yellow
7 = light grey f = white

Picking a bright color (8-f) for the background results in the corresponding dark color (0-7), with the foreground flashing."

My question is how do I insert these special codes such as ASCII12 or ASCII 15 into a text file?