The drop zone should be the whole area, all the person who tried dropped in the middle of the list, then the browser interpreted it badly and replaced the visio page by a preview of the document.
Regular drag'n'drop should be completely filtered. Add dragover / dragenter listeners + stop propagation, stop default drop behavior, just do evt.stopPropagation(); evt.preventDefault(); in the dragEnter and dragOver listeners, like in this example : http://jsbin.com/iwuleq/11/edit?html,js,output
The drop zone should be the whole area, all the person who tried dropped in the middle of the list, then the browser interpreted it badly and replaced the visio page by a preview of the document.
Regular drag'n'drop should be completely filtered. Add dragover / dragenter listeners + stop propagation, stop default drop behavior, just do evt.stopPropagation(); evt.preventDefault(); in the dragEnter and dragOver listeners, like in this example : http://jsbin.com/iwuleq/11/edit?html,js,output