Determines whether a drop is possible before the given dest_path, at the same depth as dest_path.
i.e., can we drop the data in value at that location. dest_path does not have to exist; the return value will
almost certainly be false if the parent of dest_path doesn’t exist, though.
| this |
a `GtkTreeDragDest` |
| dest_path |
destination row |
| value |
the data being dropped |
|
true if a drop is possible before |