The dropzone global attribute was introduced by the HTML5 drag and drop specification as a declarative method for specifying an HTML element's willingness to be the target of a drag-and-drop operation, the content types that can be dropped onto the element, and the drag-and-drop operation (copy/move/link). No browser has implemented the unprefixed version. Blink and WebKit implement a prefixed form of the attribute, webkitdropzone. We would like to remove the prefixed attribute.
Docs: https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/dropzone