Support drag-drop capability between the browser-based Excel online and office.js task pane apps
It's a big user interface improvement if a user and can and drop cells and data between the task pane and Excel. I found a way to get this functionality working in the Excel 2016 desktop client (and it's wonderful!) but as far as I can tell, there's no way to do it in the browser-based client. This means that I have to detect whether or not Excel is 'win32' or 'web' and then use an equivalent but much less intuitive menu-based interface for the 'web' case.