public function __construct($config = array()) {
		$defaults = array('output' => null, 'error' => null);
		$config += $defaults;

		$this->output = $config['output'];

		if (!is_resource($this->output)) {
			$this->output = fopen('php://stdout', 'r');
		}

		$this->error = $config['error'];

		if (!is_resource($this->error)) {
			$this->error = fopen('php://stderr', 'r');
		}
		parent::__construct($config);
	}