/usr/share/xsessions/xmonad.desktop is in xmonad 0.12-1.
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 | [Desktop Entry]
Name=XMonad
Comment=Lightweight tiling window manager
Exec=xmonad-session
Icon=xmonad.png
Type=XSession
|