Expanding Widgets?

I just installed Beautiful Widgets yesterday, and saw the interesting expansion capability, and was curious if anyone knows how this is done. Basically, when you tap on the weather, another window opens and displays the forecast. This is different from other weather widgets which open a full screen activity, because the home screen is still visible around the edges and in the background. Is this a transparent Activity that is being launched, or some sort of overlay or context menu, or something else?