Fix for Drag&Drop Tutorial

[franckyK]

Fix for Drag&Drop Tutorial

[ebidel]

Thanks for the report. This is an old one :)

Interested in submitting a PR? I think we should make the demo work again since a lot of content around the web references this tutorial.

[franckyK]

Indeed, the baby tut of 2010 is 7.5y old now, and in the meantime much is changed in specs and browsers. But oops, as a non-professional I've a lack of know-how for contributing substantially to an updated version.
Maybe that could be a three-stage rocket (1) a simple img dropping example, (2) file manupulation examples, and (3) this more complex arranging example.

BTW, I saw that a DnD example in the recent HTML5.2 Recommendation and in the WhatWG specification (same example) is using an empty <ol>, in which nothing can be dropped without some additions; see testpage .