<listitem><para>Credentials prefixed with <literal>systemd.extra-unit.</literal> specify additional
units to add to the final system. Note that these additional units are added to both the initrd and
the final system. <varname>ConditionPathExists=!/etc/initrd-release</varname> can be used to make
- sure the unit is conditioned out in the initrd.</para>
+ sure the unit is conditioned out in the initrd. Note that this can also be used to mask units, by
+ simply specifying an empty value.</para>
<xi:include href="version-info.xml" xpointer="v256"/></listitem>
</varlistentry>