limit of network interface name length?

Hello,

I am trying to rename a couple of interfaces, and it works for some, for 
others not.

Trying to find what I may be doing wrong, a patter that seems to emerge, 
is, that if names longer than 14Bytes are not supported. Maybe the " 
make up for the missing bytes up to 16.

F.e.:

ifconfig_epair6a_name="jail_template_local"

does not work. The interface names remaines epair6a.
Is that documented anywhere?

Or can anyone confirm this limit on solid grounds? Just to make sure I 
have not done anything other wrong.

Thanks

Ede