usually derived from glibc's
<varname>program_invocation_short_name</varname> variable, see
<citerefentry project='die-net'><refentrytitle>program_invocation_short_name</refentrytitle><manvolnum>3</manvolnum></citerefentry>.)</para>
+ <para>Note that the journal service does not validate the values of any structured
+ journal fields whose name is not prefixed with an underscore, and this includes any
+ syslog related fields such as these. Hence, applications that supply a facility, PID,
+ or log level are expected to do so properly formatted, i.e. as numeric integers formatted
+ as decimal strings.</para>
</listitem>
</varlistentry>