    public function transform($attr, $config, $context) {

        if (!isset($attr[$this->attr])) return $attr;

        $width = $this->confiscateAttr($attr, $this->attr);
        // some validation could happen here

        if (!isset($this->css[$this->attr])) return $attr;

        $style = '';
        foreach ($this->css[$this->attr] as $suffix) {
            $property = "margin-$suffix";
            $style .= "$property:{$width}px;";
        }

        $this->prependCSS($attr, $style);

        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.