Code (Javascript)

diagram.addEventListener(MindFusion.Diagramming.Events.containerChildAdding, function (sender, args)
{
	var node = args.getNode();
	var container = args.getContainer();

	// determine if the child node is a container or not.
	// or use other condition
	if (MindFusion.AbstractionLayer.isInstanceOfType(MindFusion.Diagramming.ContainerNode, node))
		args.setCancel(true);
}); 

Code (Javascript)

diagram.addEventListener(MindFusion.Diagramming.Events.nodeModified, function (sender, args)
{
  var container = args.getNode();
  if (MindFusion.AbstractionLayer.isInstanceOfType(MindFusion.Diagramming.ContainerNode, container))
  {
    var containerBounds = container.getBounds();
    var nodeAdded = false;
    for (var i = 0; i < diagram.getNodes().length; i++)
    {
      var node = diagram.getNodes()[i];
      if (node === container || node.getContainer() != null)
        continue;

      var bounds = node.getBounds();
      if (containerBounds.contains(bounds))
      {
        nodeAdded = true;
        container.add(node);
      }
    }
    if (nodeAdded)
      container.resizeToFitChildren();
  }
}); 

Code (Javascript)

var node = diagram.getNodes()[i];
if (node === container)
  continue;

var bounds = node.getBounds();

if (node.getContainer() === container)
{
  if (!containerBounds.intersectsWith(bounds))
  {
    nodeAdded = true;
    container.remove(node);
  }
}
else if (node.getContainer() != null)
  continue;
else
{
  if (containerBounds.intersectsWith(bounds))
  {
    nodeAdded = true;
    container.add(node);
  }
}