/usr/share/live/images/lxde-desktop/config/bootloaders/extlinux/menu.cfg is in live-image-lxde-desktop 4.0~a5-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | menu hshift 7
menu width 60
menu title Boot menu
include stdmenu.cfg
include live.cfg
include install.cfg
menu begin advanced
menu title Advanced options
include stdmenu.cfg
label mainmenu
menu label ^Back..
menu exit
include advanced.cfg
menu end
menu clear
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