systemd.scope and systemd.resource-control contain that link.
systemd.slice should contain it too.
<citerefentry><refentrytitle>systemd.resource-control</refentrytitle><manvolnum>5</manvolnum></citerefentry> are allowed.
</para>
+ <para>See the <ulink
+ url="http://www.freedesktop.org/wiki/Software/systemd/ControlGroupInterface/">New
+ Control Group Interfaces</ulink> for an introduction on how to make
+ use of slice units from programs.</para>
+
<para>Unless <varname>DefaultDependencies=false</varname>
is used, slice units will implicitly have dependencies of
type <varname>Conflicts=</varname> and