Insert in advanced forum: advf-forum-list.tpl.php. Please be aware of the XHTML 1.0 Strict! markup.

a) In the top after the comments insert the inline jQuery (don't know where this actually should be). This is pretty static, we should count containers from the beginning and generate the appropriate amount of jQuery (php or something). 
	<?php
	//collapsible container
	drupal_add_js (
	  
		'$(document).ready(function() {
		
		$(\'.forum-child-2\').hide(); //hide the second and third container
		$(\'.forum-child-3\').hide();

  	$(\'#containerID-1\').click(function(){$(\'.forum-child-1\').toggle()}); //make the three containers collapse when the 
  	$(\'#containerID-2\').click(function(){$(\'.forum-child-2\').toggle()});
  	$(\'#containerID-3\').click(function(){$(\'.forum-child-3\').toggle()});
		return false;
		});',
		'inline'
	);
	?>

b) After $forum_num = 0; insert this line. To have control over the container status.
	$container = 0; //collapsible container

c) Insert af the first switch:  "$position = 'middle_row';}". Increment the container ID if the "forum" is a container.
	//collapsible container
  if ($forum->is_container)
  	$container = $container +1;

d) Replace: <tr id="forum-list-<?php print $child_id; ?>" class="<?php print $forum->zebra; ?> <?php print $position;?>">. Here I added the child class for each container. Applies only for children of the container. This identifies which table rows to "show/hide".

	<tr id="forum-list-<?php print $child_id; ?>" class="<?php print $forum->zebra; ?> <?php print $position;?> <?php if (!$forum->is_container) print "forum-child-".$container;?>"> <!-- collapsible container-->
	
e) Replace: <div class="name"><a href="<?php print $forum->link; ?>"><?php print $forum->name; ?></a></div>. Here I add the show/hide span for each forum container. The css part should be moved to the css files of the adv forum module.

	<div class="name"><a href="<?php print $forum->link; ?>"><?php print $forum->name; ?></a> <?php if ($forum->is_container) print "<a href=\"#\" id=\"containerID-".$container."\" style=\"margin:0 1em 0 0; float: right;\"> show/hide</a>";?><!--collapsible container--></div>