public function clear($name = null)
    {
        if (!is_null($name)) {
            $name = strtolower($name);
            if (array_key_exists($name, self::$clearings)) {
                $this->{$name} = self::$clearings[$self::$clearings];
            }
        } else {
            foreach (self::$clearings as $n=>$v) {
                $this->{$n} = $v;
            }
        }
        return $this;
    }