protected function _bytes()
    {
        if (is_null($this->col_bytes)) {
            $a = new A();

            $this->_chars();

            while ($this->col_chars->valid()) {

                while ($this->col_chars->current()->bytes->valid()) {
                    $a->add($this->col_chars->current()->bytes->current());
                    $this->col_chars->current()->bytes->next();
                }

                $this->col_chars->next();
            }
            $this->col_bytes = $a;
            unset($a);
        }

        return $this->col_bytes;
    }