public static function relativeTo($from, $to) {
        if (static::isRelative($from) || static::isRelative($to)) {
            throw new InvalidArgumentException('Cannot determine relative path without two absolute paths');
        }

        $ds = static::SEPARATOR;
        $from = explode($ds, static::ds($from, true));
        $to = explode($ds, static::ds($to, true));
        $relative = $to;

        foreach ($from as $depth => $dir) {
            // Find first non-matching dir and ignore it
            if ($dir === $to[$depth]) {
                array_shift($relative);

            // Get count of remaining dirs to $from
            } else {
                $remaining = count($from) - $depth;

                // Add traversals up to first matching dir
                if ($remaining > 1) {
                    $padLength = (count($relative) + $remaining - 1) * -1;
                    $relative = array_pad($relative, $padLength, '..');
                    break;
                } else {
                    $relative[0] = '.' . $ds . $relative[0];
                }
            }
        }

        if (!$relative) {
            return '.' . $ds;
        }

        return implode($ds, $relative);
    }