* Subclasses may implement this to determine the necessary updates more
* efficiently, or make use of information about the old content.
*
+ * @note Implementations should call the SecondaryDataUpdates hook, like
+ * AbstractContent does.
+ *
* @param Title $title The context for determining the necessary updates
* @param Content $old An optional Content object representing the
* previous content, i.e. the content being replaced by this Content