doc.silverstripe.org/sapphire/javascript/SelectionGroup.js

(function($) {
$(document).ready(function() {
	$('ul.SelectionGroup input.selector').live('click', function(){
		var li = $(this).parent('li')
		li.addClass('selected');
		
		var prev = li.prevAll('li.selected');
		if(prev.length) prev.removeClass('selected');
		var next = li.nextAll('li.selected');
		if(next.length) next.removeClass('selected');
		
		$(this).focus();
	});
})
})(jQuery);