/usr/share/mate-power-manager/ui/brightness-applet-menu.xml is in mate-power-manager-common 1.12.1-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | <menuitem name="Help" action="Help" />
<menuitem name="About" action="About" />
|