public static String addGroupToPubSub(String group, String inputChannelName) {
		if (inputChannelName.startsWith(TAP_CHANNEL_PREFIX)
				|| inputChannelName.startsWith(TOPIC_CHANNEL_PREFIX)) {
			inputChannelName = group + "." + inputChannelName;
		}
		return inputChannelName;
	}
The prefix for the consumer/producer when creating a topic.
spring-xd-messagebus-spi/src/main/java/org/springframework/xd/dirt/integration/bus/BusUtils.java