Are IE7 and 8 modes in IE9 the real thing?

Question

I just want to know if IE7 and IE8 modes in the F12 toolbar menus are actually using IE7 and IE8 to render pages and if there are any differences between them and their standalone counterparts?

Answer 1

There are differences. From my understanding, you really can't rely on them for JavaScript because IE9 will still use its IE9 JS engine, rather than the true ones from IE7 and IE8. And I'm sure even the rendering engines aren't 100% accurate.

In all my searching for the holy grail of IE testing, there only one thing that you can truly depend on: testing actually on a Windows OS running that browser. Microsoft offers a program called Virtual PC and provides downloads for virtual discs that contain different versions of Windows & IE.

If you really want accuracy, this is the only way to go.