StupidScript - 9:43 pm on Nov 17, 2011 (gmt 0)
Well ... wasn't that fun?
I decided to try something I hadn't tried ... and I got it. The toolbar button needs to have both "ondragenter" and "ondragover" event handlers set to "preventDefault()" in order to make the button a drop target. Once done, whatever is dropped onto it will reveal its secrets.