This signal is emitted when the user has dragged something
from one widget and dropped it onto another widget. The data
to be transferred from one to another widget is requested
via this signal.
To set the data, use the set()
function of the selection.
Example 60. Passing drag data to the drop target
function dnd_drag_data_get($widget, $context, $selection_data, $info, $time)
{
$dnd_string = "Perl is the only language that looks\nthe same before and after RSA encryption";
$selection_data->set($selection_data->target, 8, $dnd_string);
}