Open an app in a window? Doesn't work for me.

This page says “Open an app in a window: While working with other apps in windows, drag the app icon to the center of the screen. If it was previously full screen, it opens as a windowed app, and if it was previously resized, it opens in its previous size.” Nothing like this happens for me; the app just comes up in the configuration it was last in. What am I missing? They don't say where you're supposed to be able to drag from; I assumed the Dock.