DragOver Event
A DragOver event occurs during a drag-and-drop operation when the mouse cursor is moved over a field that will accept the object being dragged. A DragOver event also occurs if the mouse is over a TreeviewField, a ListviewField, or a TableField, and the mouse movement causes the field to scroll.
on dragover [activefieldname]
activefieldname is unnecessary if the statement is in a field script.