the method is called when an item is moved into a possible drop landing during dnd
| source | HTMLElement | a DOM element on which a dnd action started |
| target | HTMLElement | a DOM element of a possible drop landing |
| ev | Event | a native HTML event |
| HTMLElement | a DOM element which will be saved as a drop target (to ignore a drop landing, return a null value) |
The method isn't purposed for direct call! It is an extension point.
You can override it with your own logic, but check drag-n-drop related events first, as they provide a much more convenient way for drag-n-drop handling.