var list = document.getElementsByTagName("li");
function markSelection() {
if(list[0].style.fontWeight !== "bold") {
list[0].style.fontWeight = "bold";
} else {
list[0].style.fontWeight = "normal";
}
}
for (i = 0, len = list.length; i < len; i++){
list[i].onclick = markSelection;
}