UtfSafeString::escapeInvalidUtf

static function escapeInvalidUtf($string)
{
	$escape = function($matches)
	{
		return (isset($matches[2])? '?' : $matches[1]);
	};

	return preg_replace_callback('/([x00-x7F]+
		|[xC2-xDF][x80-xBF]
		|xE0[xA0-xBF][x80-xBF]|[xE1-xECxEExEF][x80-xBF]{2}|xED[x80-x9F][x80-xBF])
		|([x80-xFF])/x', $escape, $string
	);
}