I pushed updates.  I declined two changes and wanted to point them out:

>  (defun dslide--list-item-contains (item loc)
> -  (when item
> -    (let ((beg (car item))
> -          (end (car (last item))))
> -      (and  (>= loc beg)
> -            (< loc end)))))
> +  (and item (<= (car item) loc (+ (car (last item))))))

I omitted the call to `+'.  No idea what it could do there.  `item' is an org item, which will always contain an integer in this situation.

I did not use `message--max' because it produced a compiler warning.