How to change height of iframe based on dynamic conent within the iframe?

Question

I have an iframe that has dynamic content. If the answers specific questions, additional information displays (hidden div becomes visible). I\'d like the height of the iframe

Answer 1

Esailija's answer works fine, but this is nicer imo.

$('#ifr').contents($(".toggle_div")).bind("change", function () {
    $("#ifr").height($("#ifr").contents().find("html").height());
});