protected function parseMobiHeader()
    {
        if (!$this->palmDocHeader) {
            return;
        }
        $file = $this->file;
        $this->mobiHeaderStart = $file->ftell() + 2;
        $file->fseek($this->mobiHeaderStart);
        if ($file->fread(4) === 'MOBI') {
            $this->mobiHeader = new MobiHeader(
                $this->readData($file, 4),
                $this->readData($file, 4),
                $this->readData($file, 4),
                $this->readData($file, 4),
                $this->readData($file, 4)
            );
        }
        $file->fseek($this->mobiHeaderStart + 68);
        $data = $file->fread(8);
        $title = unpack('N*', $data);
        $file->fseek($this->mobiHeaderStart + ($title[1] - 16));
        $this->title = $file->fread($title[2]);
    }