public function xmlOutput() {
        $o = '';
        $o.= '        <INDEX NAME="' . $this->name . '"';
        if ($this->unique) {
            $unique = 'true';
        } else {
            $unique = 'false';
        }
        $o.= ' UNIQUE="' . $unique . '"';
        $o.= ' FIELDS="' . implode(', ', $this->fields) . '"';
        if ($this->hints) {
            $o.= ' HINTS="' . implode(', ', $this->hints) . '"';
        }
        if ($this->comment) {
            $o.= ' COMMENT="' . htmlspecialchars($this->comment) . '"';
        }
        $o.= '/>' . "\n";

        return $o;
    }