/usr/share/xsessions/blackbox.desktop is in blackbox 0.70.1-23+deb8u1.
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 | [Desktop Entry]
Encoding=UTF-8
Name=Blackbox
Comment=Highly configurable and low resource X11 Window manager
Exec=blackbox
Terminal=False
TryExec=blackbox
Icon=blackbox.xpm
Type=Application
[Window Manager]
SessionManaged=true
|