It's pretty close - but not the same, there are a few subtle differences.
It all depends on your code ... for example. if your pages are not of type doctype, for example. if you work in quirks mode or use quirks mode, the interpretation of height="100%" in the iframe is different from the actual IE7 versus IE7mode in IE8. The first is "100% of my container", later - "100% of the default height", which is about 220 pixels.
source share