$title: Current Title object being displayed in search results.
&$id: Revision ID (default is false, for latest)
+'SearchIndexFields': Add fields to search index mapping.
+&$fields: Array of fields, all implement SearchIndexField
+$engine: SearchEngine instance for which mapping is being built.
+
+'SearchDataForIndex': Add data to search document. Allows to add any data to
+the field map used to index the document.
+&$fields: Array of name => value pairs for fields
+$handler: ContentHandler for the content being indexed
+$page: WikiPage that is being indexed
+$output: ParserOutput that is produced from the page
+$engine: SearchEngine for which the indexing is intended
+
'SecondaryDataUpdates': Allows modification of the list of DataUpdates to
perform when page content is modified. Currently called by
AbstractContent::getSecondaryDataUpdates.