FluentDOM\Xpath::quote PHP Method

    public function quote($string)
    {
        $string = str_replace("", '', $string);
        $hasSingleQuote = FALSE !== strpos($string, "'");
        if ($hasSingleQuote) {
            $hasDoubleQuote = FALSE !== strpos($string, '"');
            if ($hasDoubleQuote) {
                $result = '';
                preg_match_all('("[^\']*|[^"]+)', $string, $matches);
                foreach ($matches[0] as $part) {
                    $quoteChar = substr($part, 0, 1) === '"' ? "'" : '"';
                    $result .= ", " . $quoteChar . $part . $quoteChar;
                }
                return 'concat(' . substr($result, 2) . ')';
            } else {
                return '"' . $string . '"';
            }
        } else {
            return "'" . $string . "'";
        }
    }