Only one version of Internet Explorer (IE) can exist on a single windows installation by default. I had previously used Multiple IE as a way of testing web pages on older versions of IE. This allows you to have IE3, IE4, IE5, IE5.5, and IE6 installed alongside your existing IE7 or IE8 install. You can even run them concurrently.
I don’t test pages on anything earlier than IE6 anymore, but IE6 still accounts for more than 5% of my site traffic. Multiple IE basically helps me test both IE6 and IE8 from the same machine. However, there is still the IE7 gap, plus Multiple IE, which is no longer being updated or maintained, can produce some glitchy behavior.
It turns out, though, Microsoft offers some tools to help test their legacy browsers.
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