ChildDragOver Event
The ChildDragOver event occurs during a drag-and-drop operation when the mouse cursor is moved over a field that accepts the object being dragged. A ChildDragOver 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 childdragover [compositefieldname]
Specifying compositefieldname causes the event to be generated only for the children of the specified composite field.