(UPDATE 1 Oct 2014 Due to a change in how macros work in Debug Mode, the {{generic event handler}} macro no longer works when testing in Debug Mode. That means that you’ll have to test your custom listener in a live container (I know, ouch!). If you want to test in Debug Mode, you’ll have to skip using the {{generic event handler}} as a macro, and instead copy the inner function into the Custom HTML Tag, give the function a name, and use that as the callback in addEventListener or attachEvent.
