public function getString($type = 'letter', $desired_length = null)
	{
		if (empty($desired_length)) {
			$desired_length = $this->getInteger(1, 50);
		}
		
		$result = '';
		
		while (strlen($result) < $desired_length) {
			if ($type == 'letter') {
				$result .= $this->getLetter();
			} elseif ($type == 'number') {
				$result .= $this->getInteger(1, 10);
			} else {
				// Mix letters/numbers.
				$result .= $this->getUniqueHash();
			}
		}
		
		return substr($result, 0, $desired_length);
	}