which types of default drag behavior to use
a pointer to an array of gtk.TargetEntrys indicating the drop types that this widget will accept, or NULL. Later you can access the list with gtk_drag_dest_get_target_list() and gtk_drag_dest_find_target().
a bitmask of possible actions for a drop onto this widget.
Sets a widget as a potential drop destination, and adds default behaviors.
The default behaviors listed in flags have an effect similar to installing default handlers for the widget’s drag-and-drop signals (drag-motion, drag-drop, ...). They all exist for convenience. When passing GTK_DEST_DEFAULT_ALL for instance it is sufficient to connect to the widget’s drag-data-received signal to get primitive, but consistent drag-and-drop support.
Things become more complicated when you try to preview the dragged data, as described in the documentation for drag-motion. The default behaviors described by flags make some assumptions, that can conflict with your own signal handlers. For instance GTK_DEST_DEFAULT_DROP causes invokations of gdk_drag_status() in the context of drag-motion, and invokations of gtk_drag_finish() in drag-data-received. Especially the later is dramatic, when your own drag-motion handler calls gtk_drag_get_data() to inspect the dragged data.
There’s no way to set a default action here, you can use the drag-motion callback for that. Here’s an example which selects the action to use depending on whether the control key is pressed or not: