Should add this category to the store. The second parameter is the value for numberOfItems.
List of Items to be categorized
Collection Count Summary
You can't drop items onto this tree, but you can reorder categories. The between threshold is set to 5, so if you are near the top or bottom of a node the drop will be above or below it.
Drop items from above list onto this tree, but only on to categories; should fail to let you drop on other items. Can also move items within this tree. The drag threshold is set to 8, so you have a few pixels of buffer before drag operations start.