Someone

function hide_spans(parent, className)
{
	var tags = parent.getElementsByTagName("SPAN");
	var i, len = tags.length;
	
	for (i = 0; i < len; i++)
		if (tags[i].className == className)
			tags[i].style.display = "none";
}

function show_spans(parent, className)
{
	var tags = parent.getElementsByTagName("SPAN");
	var i, len = tags.length;
	
	for (i = 0; i < len; i++)
		if (tags[i].className == className)
			tags[i].style.display = "";
}

hide_spans( document.getElementById("my_div_id") , "lines" );