how to use labels in loader.conf file on 8.1 (syntax error)

[Michal]

Hello.

How to specify some providers by their label in loader.conf file?

geom_label_load="YES"
geom_eli_load="YES"
geli_label/private_keyfile0_load="YES"
geli_label/private_keyfile0_type="label/private:geli_keyfile0"
geli_label/private_keyfile0_name="/boot/keys/private.key0"


Now system doesn't boot up at all. It says:

Loading /boot/defaults/loader.conf
Warning: syntax error on file /boot/loader.conf
geli_label/private_keyfile0_load="YES"
          ^
Unable to load a kernel!
-
can't load 'kernel'


So it looks to me that it simply doesn't like slashes. What is the proper 
way of doing it?
Keep in mind that in this situation I can not use provider's name (i.e. 
ad0s2) because then geli would fail at later stage (as I understand it).

Thank you in advance.
Michal