onDragOver property

ElementStream<MouseEvent> onDragOver
@DocsEditable(), @DomName('Element.ondragover')

A stream of dragover events fired when a dragged object is currently being dragged over this element.

Other resources

Drag and drop sample based on the tutorial from HTML5Rocks. Drag and drop specification from WHATWG.

Implementation 

@DomName('Element.ondragover')
@DocsEditable()
ElementStream<MouseEvent> get onDragOver;