Himmel also have a config file for immutable things in project, like dialog box texture, window name, screen resolution, or default fullscreen.

If you already know how it works, you can look into Lua API reference

For example:

TITLE:I/O Revision II
SCRIPT:scripts/KO00.lua
DIALOG_END_INDICATOR:res/misc/circle.png
DIALOG_BOX:res/misc/win_01b.PNG
FALLBACK_FONT:res/font_en.png
ICON:res/icon.png
DEV_SCREEN_WIDTH:1344
DEV_SCREEN_HEIGHT:1008
SCREEN_WIDTH:640
SCREEN_HEIGHT:480
DEFAULT_FULLSCREEN:false

Let's break down every point, but before we start i wanna say that any string may contain spaces and path size not restricted.

TITLE:

Specifies window title(what is written at top window border). Its a string.

SCRIPT:

Initial Lua script, which executes after menu. If there is logic for loading saves, it would be not used after save.

DIALOG_END_INDICATOR:

What you see at line's end when all text has been typed.

DIALOG_BOX:

Dialog box texture path.

FALLBACK_FONT:

Default font, which would be used if loadFont() fails. If not specified, raylib font would be used.

DEV_SCREEN_WIDTH:

Size of window, with which you've developed game. It used for proper scaling on different screen resolutions. It's integer value.

DEV_SCREEN_HEIGHT:

Same as DEFAULT_SCREEN_WIDTH, but for height. It's integer value.

SCREEN_WIDTH:

Screen width of game window. Integer value.

SCREEN_HEIGHT:

Screen height of game window. Integer value.

DEFAULT_FULLSCREEN:

Boolean or integer(0/1) value, is game starting at fullscreen or not.