I have an interesting notice on IE8 Compatibility Mode, and would like to share it with you. IE8 Compatibility Mode emulates IE7, not IE6. IE6 is not allowed to be emulated at all. So when you work in Compatibility Mode you are testing IE7. But IE7 render engine differs from IE6 a lot. There were layout violations for IE8 Compatibility Mode in some applications which I worked with, although they were working fine in pure IE8.
Luckily, you are allowed to control an accessibility of Compatibility Mode of your pages using an html meta, see below:
<!– Each of them will turn off the mode disregarding of user preferences –>
<meta http-equiv=”X-UA-Compatible” content=”IE=8″ />
<!– or –>
<meta http-equiv=”X-UA-Compatible” content=”IE=Edge” />