public function remove($startIndex, $length)
    {
        $start = UTF8::substr
        (
            (string)$this->str,
            0,
            $startIndex,
            $this->str->getEncoding()
        );

        $end = UTF8::substr
        (
            (string)$this->str,
            $startIndex + $length,
            $this->str->getLength(),
            $this->str->getEncoding()
        );

        $this->str = new Str($start.$end);

        return $this;
    }