/usr/share/xsessions/matchbox.desktop is in matchbox-common 0.9.1-6.
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 | [Desktop Entry]
Name=Matchbox
Comment=This session logs you into Matchbox
Exec=matchbox-session
Terminal=false
Icon=
Keywords=handheld;desktop;session;
Type=Application
|