gistfile1.js

var list = $$('#yourBox li');
list.each(function(elm){
	elm['keys'] = elm.innerHTML.stripTags().toLowerCase();
});
var lastValue = $F("filter");
$('filter').observe('keyup', function(e) {
	var value = this.value.toLowerCase();
	if (value !== lastValue) {
		list.each(function(elm) {
			if (elm.keys.include(value)) {
				elm.show();
			}else{
				elm.hide();
			}
		});
		lastValue = value;
	}
});