public function fetchOffset($num)
    {
        // If the content has been modified, regenerate $this->content.
        // and $this->contentKeys.
        if ($this->contentModified) {
            $this->generateContent();
        }
        
        // If the offset exists, return the data.
        $key = $this->fetchOffsetKey($num);
        if ($key != null) {
            return $this->content[$key];
        }
        
        return null;
    }