multiple nameservers in resolvconf.conf

[Igor R.]

There are the following options in resolvconf.conf:
https://www.freebsd.org/cgi/man.cgi?query=resolvconf.conf&sektion=5

append_nameservers
and
prepend_nameservers

Even though the option has "nameservers" in plural, I could not find any 
example anywhere on the net that would indicate multiple values for these 
two options.
How can one specify multiple servers in either of them?

I've tried
append_nameservers=127.0.0.1, 192.168.15.2
append_nameservers=127.0.0.1,192.168.15.2
append_nameservers=127.0.0.1 192.168.15.2
append_nameservers=127.0.0.1; 192.168.15.2
as well as specifying them on separate lines:
append_nameservers=127.0.0.1
append_nameservers=192.168.15.2

These different version yield 3 different outcomes, but none of them 
produces resolv.conf 
(upon running resolvconf -u) with both servers in there.

(Not that it matters, but there is an active information from dhcp 
server/client. Tested on 10.* system.)

Thank you in adavnce,

Igor