Alex L. said: IE is often late to the party in implementing
the more cutting edge stuff from HTML 5 and has a bad history for deviating
significantly from the spec. Interestingly, the HTML5 drag-and-drop specification is based on the drag-and-drop interface that Microsoft introduced with IE5. The current spec basically lets you create a map with the datatype as the key in a map and data as the associated value -- and if the datatype is an actual MIME type (instead of a "custom" type), you can potentially drag information outside the window/tab it's originating in. Internet Explorer... still only permits the types "string" and "url". Their DND interface hasn't changed at all since IE5. That said, IE isn't the only one to deviate from the spec. The other major browsers have a lot of deviations, although generally to the effect of "handle idiots who can't write HTML correctly and still render something legible despite them", or implementing features still up for discussion and not officially a part of the specification (which is where you get vendor-prefixed CSS properties from).