public static function delete($instance)
	{
		$class = get_called_class();

		if ($instance === true)
		{
			static::$_instances[$class] = array();

			return true;
		}
		elseif (static::exists($instance))
		{
			unset(static::$_instances[$class][$instance]);

			return true;
		}

		return false;
	}