Constant OVERLAY_KEYCODES 

const OVERLAY_KEYCODES: [u32; 47];

Overlay keycodes: the main block’s character keys, 1 to /. A client may take a keycode for the physical key it names before, or instead of, the keysym the keymap gives it: Chromium drops a key whose code names no key it knows, and runs its browser, media, and launcher keys as commands, so a character bound to a spare vendor keycode is lost, or navigates the page. The character keys are the ones every layout remaps, and this keymap is the virtual keyboard’s own, so rebinding them leaves the user’s keyboard be. Under the X11 255 ceiling for XWayland apps.