Manual:Hooks/MediaWikiPerformAction

Details
Use this to do something completely different, after the basic globals have been set up, but before ordinary actions take place.
 * $output: $wgOut (OutputPage  class)
 * $article: $wgArticle (Article class)
 * $title:  $wgTitle (Title class)
 * $user:   $wgUser (User class)
 * $request: $wgRequest (WebRequest class)
 * $wiki:   MediaWiki object, added in 1.13

Note: To prevent the standard performAction class from doing anything, return false from this hook.