Originally Posted by
noonnope
which ever (i mean having a doctype or not, or having a doctype and using the developer tool to switch to quirks mode). by using developer tool you can choose to see how ie7 handles quirks mode or how ie8 handles it.
You can use compatibility view to get a rough idea of what IE7 will look like but it's not 100% accurate and misses some bugs in IE7 which would be the main reason for using it. The same applies with the Developer tools options.
None of the options recognise this IE7 bug.
Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>IE7 general sibling selector (~) bug 1</title>
<style type="text/css">
/* The ruleset below (empty or otherwise) is required for the bug! */
.holder b {
}
.holder ~ span b {
background: red;
}
</style>
</head>
<body>
<div class="holder">
<i>
<!-- HTML COMMENT OR ANY ELEMENT -->
<span>
<span><b>My background shouldn’t be red!</b></span>
</span>
</i>
</div>
</body>
</html>
Therefore I could never trust it as I test in different browers to find bugs not ignore them 
It's ok for a rough idea and useful for a quick check but don;t rely on it. (Unlike IEtester which Ryan mentioned above and spots the bug correctly.)
Note that the quirks mode option in IE8 makes IE render in quirks mode which will be similar to IE5 but again not accurate enough for any real testing. There is no option to emulate ie6.
All in all it's more a fiasco than a help. It introduces three or four more rendering inconsistencies to deal with.
There are many other options with the emulate tags also (none of which actually provide a true rendering of a browser version unfortunately.)
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