drag destination widget
drag context
list of droppable targets, or NULL to use gtk_drag_dest_get_target_list (widget). Looks for a match between the supported targets of context and the dest_target_list, returning the first matching target, otherwise returning GDK_NONE. dest_target_list should usually be the return value from gtk_drag_dest_get_target_list(), but some widgets may have different valid targets for different parts of the widget; in that case, they will have to implement a drag_motion handler that passes the correct target list to this function. [allow-none]
first target that the source offers and the dest can accept, or GDK_NONE. [transfer none]