I have the following code from the example plugin (plugin sdk).

int ts3plugin_onTextMessageEvent(uint64 serverConnectionHandlerID, anyID targetMode, anyID toID, anyID fromID, const char* fromName, const char* fromUniqueIdentifier, const char* message, int ffIgnored) {
    printf("PLUGIN: onTextMessageEvent %llu %d %d %s %s %d\n", (long long unsigned int)serverConnectionHandlerID, targetMode, fromID, fromName, message, ffIgnored);

	/* Friend/Foe manager has ignored the message, so ignore here as well. */
	if(ffIgnored) {
		return 0; /* Client will ignore the message anyways, so return value here doesn't matter */

#if 0
		/* Example code: Autoreply to sender */
		/* Disabled because quite annoying, but should give you some ideas what is possible here */
		/* Careful, when two clients use this, they will get banned quickly... */
		anyID myID;
		if(ts3Functions.getClientID(serverConnectionHandlerID, &myID) != ERROR_ok) {
			ts3Functions.logMessage("Error querying own client id", LogLevel_ERROR, "Plugin", serverConnectionHandlerID);
			return 0;
		if(fromID != myID) {  /* Don't reply when source is own client */
			if(ts3Functions.requestSendPrivateTextMsg(serverConnectionHandlerID, "Text message back!", fromID, NULL) != ERROR_ok) {
				ts3Functions.logMessage("Error requesting send text message", LogLevel_ERROR, "Plugin", serverConnectionHandlerID);

    return 0;  /* 0 = handle normally, 1 = client will ignore the text message */
But what I want is to know, how I can activate this code.
One line: "disabled, beacause quite annoying".
So how I can enable it?