The javascript below targets the span element and inserts a simple message,

function helloworld() {
	if (!document.getElementById || !document.createTextNode) {
		return;
	}
	var myMessage = 'Hello World';
	var todayDate = new Date();
	var messageContainer = document.getElementsByTagName('span')[0];
	if (!messageContainer) {
		return;
	}
	else {
		myMessage += '. Today is ';
		myMessage += todayDate.toString();
		messageContainer.firstChild.nodeValue= myMessage;
	}
}
window.onload = helloworld;	

If you have javascript enabled the message appears below: