&$langCode: the language code to get the message for (string) - or -
whether to use the content language (true) or site language (false) (bool)
+'NotifyOnPageChangeComplete': called after user email notification.
+$EmailNotification: EmailNotification object being used
+$watchingUser: user (object) to whom email was sent
+
'OpenSearchUrls': Called when constructing the OpenSearch description XML.
Hooks can alter or append to the array of URLs for search & suggestion formats.
&$urls: array of associative arrays with Url element attributes