Sets up a widget so that GTK+ will start a drag operation when the user clicks and drags on the widget.
The widget must have a window.
| this |
a Widget |
| start_button_mask |
the bitmask of buttons that can start the drag |
| targets |
the table of targets that the drag will support, may be null |
| actions |
the bitmask of possible actions for a drag from this widget |
| n_targets |
the number of items in |