var elem = "p";
window.onload = function() {
if(document.getElementsByTagName) {
var el = document.getElementsByTagName(elem);
for(var i=0; i<el.length; i++) {
if(el[i].childNodes[0].tagName != "p"
&& el[i].parentNode.className.indexOf("pbox") != -1) {
if(i%2 == 1) {
el[i].className = "on";
} else {
el[i].className = "off";
}
}
}
}
}