                $this->mode = ($this->head_pointer === null)
                    ? self::BEFOR_HEAD
                    : self::AFTER_HEAD;

                break;

            /* 15. If last is true, then set the insertion mode to "in body"
            and    abort these steps. (innerHTML case) */
            } elseif($last) {
                $this->mode = self::IN_BODY;
                break;
            }
        }
    }
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.