/***
http://www.siteduzero.com/tutoriel-3-37795-creer-un-menu-horizontal-deroulant-en-css.html
***/
sfHover = function() {
        var sfEls = document.getElementById("header_menu").getElementsByTagName("LI");
        for (var i=0; i<sfEls.length; i++) {
                sfEls[i].onmouseover=function() {
                        this.className+=" sfhover";
                }
                sfEls[i].onmouseout=function() {
                        this.className=this.className.replace(new RegExp(" sfhover\\b"), "");
                }
        }
}
if (window.attachEvent) window.attachEvent("onload", sfHover);