Flash Question

I'm copying Motion Tweens to Actionscript Code but the number of layers in my application is expanding rapidly.

I see I can insert a Timeline folder in order to organize my layers. The documentation says:

"A timeline folder would simply be a visual way to group layers inside folders. This way a 100 layers could be displayed as a single folder layer if necessary. Vertical screen estate is very valuable in the days of wide screen displays, and this would help make better use of it."

How do I get a layer below my folder to be inserted into my folder? Drag and drop does not seem to work.

Thanks,