The tool runs an isolated D-Bus session, but it also passes D-Bus
messages between the "parent" D-Bus session and the isolated
D-Bus session. It can be used for example by Flatpak applications
to run an isolated D-Bus session for recent evolution-data-server
D-Bus services, while still being able to talk to requested
D-Bus interfaces from the "parent" D-Bus session.

Its build can be enabled with -DENABLE_DBUS_SESSION_TOOL=ON CMake
command argument.