Conditional comments allow special syntax constructions for checking the IE version and are proprietary to Internet Explorer for Windows. A conditional comment is an HTML element that, in IE may conditionally be read, but, to all other browsers looks like an HTML comment and is ignored.
<!--[if IE ]> <body class="ie"> <![endif]--> <!--[if !IE]>--> <body> <!--<![endif]--> <!--[if lt IE 7 ]> <html class="ie6"> <![endif]--> <!--[if IE 7 ]> <html class="ie7"> <![endif]--> <!--[if IE 8 ]> <html class="ie8"> <![endif]--> <!--[if IE 9 ]> <html class="ie9"> <![endif]--> <!--[if (gt IE 9)|!(IE)]><!--> <html> <!--<![endif]-->