code: function sendToMultiple(send, msg, destinations, type) {
    destinations = destinations instanceof Array && destinations || [destinations];
    destinations.forEach(function(destination) {
      var set, socketIds;
      set = subscriptions[type];
      if ((socketIds = set.members(destination))) {
        return socketIds.slice(0).forEach(function(socketId) {
          if (!send.socketId(socketId, msg, destination)) {
            return set.removeFromAll(socketId);
          }
        });
      }
    });
    return true;
  }
docs: Private Attempt to send the event to the socket. If socket no longer exists, remove it from set