pocketmine\nbt\tag\ListTag::offsetGet PHP Method

    public function offsetGet($offset)
    {
        if (isset($this->{$offset}) and $this->{$offset} instanceof Tag) {
            if ($this->{$offset} instanceof \ArrayAccess) {
                return $this->{$offset};
            } else {
                return $this->{$offset}->getValue();
            }
        }
        return null;
    }