CEP: Drag and Drop between Premiere and Extension

I want the user to be able to drag video items from Media Browser to the extension panel. And here is my ondrop callback of the html element:

function drop(ev) {
     ev.preventDefault();
     var data = ev.dataTransfer;
     alert('data.files.length : '+data.files.length);
     alert('data.items.length : '+data.items.length);
}

Result:

data.files.length : 0
data.items.length : 0

Question:

How can I know which video item was draged ? Is it possible at all ?