[syslog-ng] mark-freq() and mark-mode() understanding

[Sergey Y. Afonin]

Hello.

I need an explanation of  mark-freq() and mark-mode() works.

=== a part of syslog-ng.conf ===
options {
	...
	mark-freq(300);
	...
	}

destination mesg	{ file("/var/log/syslog/messages" mark-mode(periodical)); };
===

=== a part of /var/log/syslog/messages ===
Jun 24 08:26:35 -- MARK --
Jun 24 08:30:01 crond[10512]: (root) CMD (   /usr/bin/freshclam --quiet --daemon-notify)
Jun 24 08:31:30 -- MARK --
Jun 24 09:01:01 crond[10544]: (root) CMD (run-parts /etc/cron.hourly)
Jun 24 09:25:30 syslog-ng[9983]: Log statistics ...
===

"MARK" label absent between 08:31:30 and 09:01:01 for example.
Does it turns out that "idle" is checked for all file() globally ?
Can I setup it for one file() ?

-- 
Regards, Sergey.