function walk($elements, $max_depth, $args = array())
{
$output = parent::walk($elements, $max_depth, $args);
$output = str_replace(array('type="checkbox"', "type='checkbox'"), array('type="radio"', "type='radio'"), $output);
return $output;
}
function start_el(&$output, $category, $depth = 0, $args = array(), $id = 0)
{
parent::start_el($output, $category, $depth, $args, $id);
$output = preg_replace('/ type="checkbox" /u', ' type="radio" ', $output);
}
