public function isDirty() {

    // If there is no content, the object can't be dirty.
    if (!isset($this->content)) {
      return FALSE;
    }

    // Content is dirty iff content is set, and it is
    // different from the original content. Note that
    // we are using the etag from the original headers.
    if ($this->etag != md5($this->content)) {
      return TRUE;
    }

    return FALSE;
  }