    public function transform($attr, $config, $context) {
        if (!isset($attr['border'])) return $attr;
        $border_width = $this->confiscateAttr($attr, 'border');
        // some validation should happen here
        $this->prependCSS($attr, "border:{$border_width}px solid;");
        return $attr;
    }
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.