fix `data-method` with IE
would be better (and faster, because element1.insert(element2) actually ends in Prototype internals as element1.appendChild(element2))
You might be right, but we're not talking about a performance bottleneck here. The overhead of the insert() method is negligible comparing to the time that's needed to actually submit the form and reload the next page.
OK, but anyway this mix of DOM & Prototype is odd-looking, at least for me. Maybe
This is even shorter than original.
With that you're right. Both forms are better than accessing parentNode