|buttonRect||The button from which the position of the window will be determined (see description).|
|windowSize||The initial size of the window.|
Shows a window with dropdown behaviour and styling.
The window is styled in the same way as a PopupWindow, which means the window is automatically closed when it loses focus, and has no frame around the edge. Note this function auto-fits the window to screen while trying to place it first below then above the button it was triggered from. This means the windowSize might change when fitting it to screen, so you should make sure you read the 'position' afterwards to check whether the size was cropped.