public int defineChannelName(String name, int value) {
		Integer prev = channelNameToValueMap.get(name);
		if (prev != null) {
			return prev;
		}

		channelNameToValueMap.put(name, value);
		setChannelNameForValue(value, name);
		maxChannelType = Math.max(maxChannelType, value);
		return value;
	}
Define a token channel with a specified name.

<p>
If a channel with the specified name already exists, the previously
assigned channel value is not altered.</p>

@param name The channel name.
@return The constant channel value assigned to the channel.
tool/src/org/antlr/v4/tool/Grammar.java