In whatwg/html@3044a7e @pwnall and @domenic removed the dropzone global attribute due to it not gaining traction.

As it turns out this feature was supposed to work together with https://drafts.csswg.org/selectors/#drag-pseudos: https://www.w3.org/TR/2013/WD-selectors4-20130502/#drag-pseudos.

Without the dropzone attribute I don't think these psuedo-classes have a hook to use, so they probably need to be removed, unless I'm missing something.

(Credit: @fantasai in #2250.)