protected static function exportString($str)
	{
		// foo becomes 'foo'
		if (strpos($str, "'") === false)
		{
			return "'" . $str . "'";
		}

		// d'oh becomes "d'oh"
		if (strpos($str, '"') === false)
		{
			return '"' . $str . '"';
		}

		// This string contains both ' and ". XPath 1.0 doesn't have a mechanism to escape quotes,
		// so we have to get creative and use concat() to join chunks in single quotes and chunks
		// in double quotes
		$toks = [];
		$c    = '"';
		$pos  = 0;
		while ($pos < strlen($str))
		{
			$spn = strcspn($str, $c, $pos);
			if ($spn)
			{
				$toks[] = $c . substr($str, $pos, $spn) . $c;
				$pos   += $spn;
			}
			$c = ($c === '"') ? "'" : '"';
		}

		return 'concat(' . implode(',', $toks) . ')';
	}