Because of some browser incompatibility, you need to have some piece of CSS on your page for a specific browser, ex: IE.
If you are using Zend Framework, it would be easy. In the controller, you can include the stylesheet / CSS using this:
$this->view->headLink()->appendStylesheet(PUBLIC_WEB_PATH . '/css/account_form_ie.css', 'all', 'IE');
The headLink() helper has the method:
appendStylesheet($href, $media, $conditionalStylesheet)
If you simply want to include a CSS file, you may ommit the media and conditionalStylesheet parameter.
The output would be:
<!--[if IE]> <link href="/daito/public/css/account_form_ie.css" media="all" rel="stylesheet" type="text/css" /> <![endif]-->
Source: http://surlandia.com/2008/02/22/conditional-stylesheet-using-headlink-placeholder-zend-framework/