the edge or corner from which the drag is started
the device used for the operation
the button being used to drag, or 0 for a keyboard-initiated drag
surface X coordinate of mouse click that began the drag
surface Y coordinate of mouse click that began the drag
timestamp of mouse click that began the drag (use [method@Gdk.Event.get_time])
Begins an interactive resize operation.
You might use this function to implement a “window resize grip.”