There is a trick for creating an element to fill the document by setting all four `top`, `right`, `bottom`, `left` properties, and letting the browser calculate the size of the element. However, it doesn't seem to apply to IFRAMEs the same as it does to block-level or inline elements (see http://jsfiddle.net/thirdender/ULHbs/). An extra DIV wrapper is necessary to make this trick work.