public function get_attribute($key = null, $default = null)
	{
		if ($key === null)
		{
			return $this->attributes;
		}

		if (is_array($key))
		{
			$output = array();
			foreach ($key as $k)
			{
				$output[$k] = array_key_exists($k, $this->attributes) ? $this->attributes[$k] : $default;
			}
			return $output;
		}

		return array_key_exists($key, $this->attributes) ? $this->attributes[$key] : $default;
	}