Allow drop to validate the dragged content

Allow drop to validate the dragged content beyond the channels information.
Here, I am trying to prevent an element to be dropped onto itself.

Since 'dragEnter' does not expose the dataTransfer value, as per 6.7.6 (link below), keeping a local copy of the latest data (in object form), to be used for comparison purposes on the 'drop-validate' attribute.
http://www.whatwg.org/specs/web-apps/current-work/multipage/dnd.html#dndevents