    public function __construct($attr) {
        $this->attr = $attr;
        if (!isset($this->css[$attr])) {
            trigger_error(htmlspecialchars($attr) . ' is not valid space attribute');
        }
    }
The software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.