Does socket.io support PUBSUB?

I did an extensive search on the web and found that most people mentioned that socket.io + redis --> pub/sub.

On the other hand, socket.io is claimed to be a realtime web service.

So my question is: does socket.io itself support PUB/SUB? If not, should I integrate socket.io with other tools(such as redis) to implement PUB/SUB?