My original post answers what you just said.
"Other modes not mentioned in the RFC are subject to the ircd developers' own opinions. +r/+R being one example. +r on an Undernet channel means registered users only may join, whereas it's +R on DALnet. I would imagine this is partly why mIRC would never be able to make an arbitrary Channel Central screen with different check boxes based on the RAW reply for channel modes, as the different letters could mean different things on different networks."
Regards,
