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[lhc/web/wiklou.git] / docs / hooks.txt

hooks.txt

This document describes how event hooks work in MediaWiki; how to add hooks for
an event; and how to run hooks for an event.

==Glossary==

event
     Something that happens with the wiki. For example: a user logs in. A wiki
     page is saved. A wiki page is deleted. Often there are two events
     associated with a single action: one before the code is run to make the
     event happen, and one after. Each event has a name, preferably in
     CamelCase. For example, 'UserLogin', 'ArticleSave', 'ArticleSaveComplete',
     'ArticleDelete'.

hook
     A clump of code and data that should be run when an event happens. This can
     be either a function and a chunk of data, or an object and a method.

hook function
     The function part of a hook.

==Rationale==

Hooks allow us to decouple optionally-run code from code that is run for
everyone. It allows MediaWiki hackers, third-party developers and local
administrators to define code that will be run at certain points in the mainline
code, and to modify the data run by that mainline code. Hooks can keep mainline
code simple, and make it easier to write extensions. Hooks are a principled
alternative to local patches.

Consider, for example, two options in MediaWiki. One reverses the order of a
title before displaying the article; the other converts the title to all
uppercase letters. Currently, in MediaWiki code, we would handle this as follows
(note: not real code, here):

        function showAnArticle($article) {
                global $wgReverseTitle, $wgCapitalizeTitle;

                if ($wgReverseTitle) {
                        wfReverseTitle($article);
                }

                if ($wgCapitalizeTitle) {
                        wfCapitalizeTitle($article);
                }

                # code to actually show the article goes here
        }

An extension writer, or a local admin, will often add custom code to the
function -- with or without a global variable. For example, someone wanting
email notification when an article is shown may add:

    function showAnArticle($article) {
        global $wgReverseTitle, $wgCapitalizeTitle, $wgNotifyArticle;

                if ($wgReverseTitle) {
                        wfReverseTitle($article);
                }

                if ($wgCapitalizeTitle) {
                        wfCapitalizeTitle($article);
                }

                # code to actually show the article goes here

                if ($wgNotifyArticle) {
                        wfNotifyArticleShow($article));
                }
        }

Using a hook-running strategy, we can avoid having all this option-specific
stuff in our mainline code. Using hooks, the function becomes:

        function showAnArticle($article) {

                if (wfRunHooks('ArticleShow', array(&$article))) {

                        # code to actually show the article goes here

                        wfRunHooks('ArticleShowComplete', array(&$article));
                }
        }

We've cleaned up the code here by removing clumps of weird, infrequently used
code and moving them off somewhere else. It's much easier for someone working
with this code to see what's _really_ going on, and make changes or fix bugs.

In addition, we can take all the code that deals with the little-used
title-reversing options (say) and put it in one place. Instead of having little
title-reversing if-blocks spread all over the codebase in showAnArticle,
deleteAnArticle, exportArticle, etc., we can concentrate it all in an extension
file:

        function reverseArticleTitle($article) {
                # ...
        }

        function reverseForExport($article) {
                # ...
        }

The setup function for the extension just has to add its hook functions to the
appropriate events:

        setupTitleReversingExtension() {
                global $wgHooks;

                $wgHooks['ArticleShow'][] = 'reverseArticleTitle';
                $wgHooks['ArticleDelete'][] = 'reverseArticleTitle';
                $wgHooks['ArticleExport'][] = 'reverseForExport';
        }

Having all this code related to the title-reversion option in one place means
that it's easier to read and understand; you don't have to do a grep-find to see
where the $wgReverseTitle variable is used, say.

If the code is well enough isolated, it can even be excluded when not used --
making for some slight savings in memory and load-up performance at runtime.
Admins who want to have all the reversed titles can add:

        require_once 'extensions/ReverseTitle.php';

...to their LocalSettings.php file; those of us who don't want or need it can
just leave it out.

The extensions don't even have to be shipped with MediaWiki; they could be
provided by a third-party developer or written by the admin him/herself.

==Writing hooks==

A hook is a chunk of code run at some particular event. It consists of:

  * a function with some optional accompanying data, or
  * an object with a method and some optional accompanying data.

Hooks are registered by adding them to the global $wgHooks array for a given
event. All the following are valid ways to define hooks:

        $wgHooks['EventName'][] = 'someFunction'; # function, no data
        $wgHooks['EventName'][] = array('someFunction', $someData);
        $wgHooks['EventName'][] = array('someFunction'); # weird, but OK

        $wgHooks['EventName'][] = $object; # object only
        $wgHooks['EventName'][] = array($object, 'someMethod');
        $wgHooks['EventName'][] = array($object, 'someMethod', $someData);
        $wgHooks['EventName'][] = array($object); # weird but OK

When an event occurs, the function (or object method) will be called with the
optional data provided as well as event-specific parameters. The above examples
would result in the following code being executed when 'EventName' happened:

        # function, no data
        someFunction($param1, $param2)
        # function with data
        someFunction($someData, $param1, $param2)

        # object only
        $object->onEventName($param1, $param2)
        # object with method
        $object->someMethod($param1, $param2)
        # object with method and data
        $object->someMethod($someData, $param1, $param2)

Note that when an object is the hook, and there's no specified method, the
default method called is 'onEventName'. For different events this would be
different: 'onArticleSave', 'onUserLogin', etc.

The extra data is useful if we want to use the same function or object for
different purposes. For example:

        $wgHooks['ArticleSaveComplete'][] = array('ircNotify', 'TimStarling');
        $wgHooks['ArticleSaveComplete'][] = array('ircNotify', 'brion');

This code would result in ircNotify being run twice when an article is saved:
once for 'TimStarling', and once for 'brion'.

Hooks can return three possible values:

  * true: the hook has operated successfully
  * "some string": an error occurred; processing should stop and the error
                   should be shown to the user
  * false: the hook has successfully done the work necessary and the calling
           function should skip

The last result would be for cases where the hook function replaces the main
functionality. For example, if you wanted to authenticate users to a custom
system (LDAP, another PHP program, whatever), you could do:

        $wgHooks['UserLogin'][] = array('ldapLogin', $ldapServer);

        function ldapLogin($username, $password) {
                # log user into LDAP
                return false;
        }

Returning false makes less sense for events where the action is complete, and
will normally be ignored.

Note that none of the examples made use of create_function() as a way to
attach a function to a hook. This is known to cause problems (notably with
Special:Version), and should be avoided when at all possible.

==Using hooks==

A calling function or method uses the wfRunHooks() function to run the hooks
related to a particular event, like so:

        class Article {
                # ...
                function protect() {
                        global $wgUser;
                        if (wfRunHooks('ArticleProtect', array(&$this, &$wgUser))) {
                                # protect the article
                                wfRunHooks('ArticleProtectComplete', array(&$this, &$wgUser));
                        }
                }
        }

wfRunHooks() returns true if the calling function should continue processing
(the hooks ran OK, or there are no hooks to run), or false if it shouldn't (an
error occurred, or one of the hooks handled the action already). Checking the
return value matters more for "before" hooks than for "complete" hooks.

Note that hook parameters are passed in an array; this is a necessary
inconvenience to make it possible to pass reference values (that can be changed)
into the hook code. Also note that earlier versions of wfRunHooks took a
variable number of arguments; the array() calling protocol came about after
MediaWiki 1.4rc1.

==Events and parameters==

This is a list of known events and parameters; please add to it if you're going
to add events to the MediaWiki code.

'AbortAutoAccount': Return false to cancel automated local account creation,
where normally authentication against an external auth plugin would be creating
a local account.
$user: the User object about to be created (read-only, incomplete)
&$abortMsg: out parameter: name of error message to be displayed to user

'AbortAutoblock': Return false to cancel an autoblock.
$autoblockip: The IP going to be autoblocked.
$block: The block from which the autoblock is coming.

'AbortDiffCache': Can be used to cancel the caching of a diff.
&$diffEngine: DifferenceEngine object

'AbortEmailNotification': Can be used to cancel email notifications for an edit.
$editor: The User who made the change.
$title: The Title of the page that was edited.
$rc: The current RecentChange object.

'AbortLogin': Return false to cancel account login.
$user: the User object being authenticated against
$password: the password being submitted, not yet checked for validity
&$retval: a LoginForm class constant to return from authenticateUserData();
          default is LoginForm::ABORTED. Note that the client may be using
          a machine API rather than the HTML user interface.
&$msg: the message identifier for abort reason (new in 1.18, not available before 1.18)

'AbortMove': Allows to abort moving an article (title).
$old: old title
$nt: new title
$user: user who is doing the move
$err: error message
$reason: the reason for the move (added in 1.13)

'AbortNewAccount': Return false to cancel explicit account creation.
$user: the User object about to be created (read-only, incomplete)
&$msg: out parameter: HTML to display on abort
&$status: out parameter: Status object to return, replaces the older $msg param (added in 1.23)
          Create the object with Status::newFatal() to ensure proper API error messages
          are returned when creating account through API clients.

'AbortTalkPageEmailNotification': Return false to cancel talk page email notification
$targetUser: the user whom to send talk page email notification
$title: the page title

'SendWatchlistEmailNotification': Return true to send watchlist email notification
$targetUser: the user whom to send watchlist email notification
$title: the page title
$enotif: EmailNotification object

'AbortChangePassword': Return false to cancel password change.
$user: the User object to which the password change is occuring
$mOldpass: the old password provided by the user
$newpass: the new password provided by the user
&$abortMsg: the message identifier for abort reason

'ActionBeforeFormDisplay': Before executing the HTMLForm object.
$name: name of the action
&$form: HTMLForm object
$article: Article object

'ActionModifyFormFields': Before creating an HTMLForm object for a page action;
Allows to change the fields on the form that will be generated.
$name: name of the action
&$fields: HTMLForm descriptor array
$article: Article object

'AddNewAccount': After a user account is created.
$user: the User object that was created. (Parameter added in 1.7)
$byEmail: true when account was created "by email" (added in 1.12)

'AddNewAccountApiForm': Allow modifying internal login form when creating an account via API.
$apiModule: the ApiCreateAccount module calling
$loginForm: the LoginForm used

'AddNewAccountApiResult': Modify API output when creating a new account via API.
$apiModule: the ApiCreateAccount module calling
$loginForm: the LoginForm used
&$result: associative array for API result data

'AfterFinalPageOutput': Nearly at the end of OutputPage::output() but
before OutputPage::sendCacheControl() and final ob_end_flush() which
will send the buffered output to the client. This allows for last-minute
modification of the output within the buffer by using ob_get_clean().
$output: The OutputPage object where output() was called

'AfterImportPage': When a page import is completed.
$title: Title under which the revisions were imported
$origTitle: Title provided by the XML file
$revCount: Number of revisions in the XML file
$sRevCount: Number of successfully imported revisions
$pageInfo: associative array of page information

'AfterParserFetchFileAndTitle': After an image gallery is formed by Parser,
just before adding its HTML to parser output.
$parser: Parser object that called the hook
$ig: Gallery, an object of one of the gallery classes (inheriting from
ImageGalleryBase)
$html: HTML generated by the gallery

'AlternateEdit': Before checking if a user can edit a page and before showing
the edit form ( EditPage::edit() ). This is triggered on &action=edit.
$editPage: the EditPage object

'AlternateEditPreview': Before generating the preview of the page when editing
( EditPage::getPreviewText() ).
$editPage: the EditPage object
&$content: the Content object for the text field from the edit page
&$previewHTML: Text to be placed into the page for the preview
&$parserOutput: the ParserOutput object for the preview
return false and set $previewHTML and $parserOutput to output custom page
preview HTML.

'AlternateUserMailer': Called before mail is sent so that mail could be logged
(or something else) instead of using PEAR or PHP's mail(). Return false to skip
the regular method of sending mail.  Return a string to return a php-mail-error
message containing the error. Returning true will continue with sending email
in the regular way.
$headers: Associative array of headers for the email
$to: MailAddress object or array
$from: From address
$subject: Subject of the email
$body: Body of the message

'APIAfterExecute': After calling the execute() method of an API module. Use
this to extend core API modules.
&$module: Module object

'ApiBeforeMain': Before calling ApiMain's execute() method in api.php.
&$main: ApiMain object

'ApiCheckCanExecute': Called during ApiMain::checkCanExecute. Use to further
authenticate and authorize API clients before executing the module. Return
false and set a message to cancel the request.
$module: Module object
$user: Current user
&$message: API usage message to die with, as a message key or array
as accepted by ApiBase::dieUsageMsg.

'APIEditBeforeSave': Before saving a page with api.php?action=edit, after
processing request parameters. Return false to let the request fail, returning
an error message or an <edit result="Failure"> tag if $resultArr was filled.
$editPage : the EditPage object
$text : the new text of the article (has yet to be saved)
&$resultArr : data in this array will be added to the API result

'APIGetAllowedParams': Use this hook to modify a module's parameters.
&$module: ApiBase Module object
&$params: Array of parameters
$flags: int zero or OR-ed flags like ApiBase::GET_VALUES_FOR_HELP

'APIGetDescription': Use this hook to modify a module's description.
&$module: ApiBase Module object
&$desc: Array of descriptions

'APIGetParamDescription': Use this hook to modify a module's parameter
descriptions.
&$module: ApiBase Module object
&$desc: Array of parameter descriptions

'APIGetResultProperties': Use this hook to modify the properties in a module's
result.
&$module: ApiBase Module object
&$properties: Array of properties

'APIGetPossibleErrors': Use this hook to modify the module's list of possible
errors.
$module: ApiBase Module object
&$possibleErrors: Array of possible errors

'APIQueryAfterExecute': After calling the execute() method of an
action=query submodule. Use this to extend core API modules.
&$module: Module object

'APIQueryGeneratorAfterExecute': After calling the executeGenerator() method of
an action=query submodule. Use this to extend core API modules.
&$module: Module object
&$resultPageSet: ApiPageSet object

'APIQueryInfoTokens': Use this hook to add custom tokens to prop=info. Every
token has an action, which will be used in the intoken parameter and in the
output (actiontoken="..."), and a callback function which should return the
token, or false if the user isn't allowed to obtain it. The prototype of the
callback function is func($pageid, $title), where $pageid is the page ID of the
page the token is requested for and $title is the associated Title object. In
the hook, just add your callback to the $tokenFunctions array and return true
(returning false makes no sense).
$tokenFunctions: array(action => callback)

'APIQueryRevisionsTokens': Use this hook to add custom tokens to prop=revisions.
Every token has an action, which will be used in the rvtoken parameter and in
the output (actiontoken="..."), and a callback function which should return the
token, or false if the user isn't allowed to obtain it. The prototype of the
callback function is func($pageid, $title, $rev), where $pageid is the page ID
of the page associated to the revision the token is requested for, $title the
associated Title object and $rev the associated Revision object. In the hook,
just add your callback to the $tokenFunctions array and return true (returning
false makes no sense).
$tokenFunctions: array(action => callback)

'APIQueryRecentChangesTokens': Use this hook to add custom tokens to
list=recentchanges. Every token has an action, which will be used in the rctoken
parameter and in the output (actiontoken="..."), and a callback function which
should return the token, or false if the user isn't allowed to obtain it. The
prototype of the callback function is func($pageid, $title, $rc), where $pageid
is the page ID of the page associated to the revision the token is requested
for, $title the associated Title object and $rc the associated RecentChange
object. In the hook, just add your callback to the $tokenFunctions array and
return true (returning false makes no sense).
$tokenFunctions: array(action => callback)

'APIQuerySiteInfoGeneralInfo': Use this hook to add extra information to the
sites general information.
$module: the current ApiQuerySiteInfo module
&$results: array of results, add things here

'APIQuerySiteInfoStatisticsInfo': Use this hook to add extra information to the
sites statistics information.
&$results: array of results, add things here

'APIQueryUsersTokens': Use this hook to add custom token to list=users. Every
token has an action, which will be used in the ustoken parameter and in the
output (actiontoken="..."), and a callback function which should return the
token, or false if the user isn't allowed to obtain it. The prototype of the
callback function is func($user) where $user is the User object. In the hook,
just add your callback to the $tokenFunctions array and return true (returning
false makes no sense).
$tokenFunctions: array(action => callback)

'ApiMain::onException': Called by ApiMain::executeActionWithErrorHandling() when
an exception is thrown during API action execution.
$apiMain: Calling ApiMain instance.
$e: Exception object.

'ApiRsdServiceApis': Add or remove APIs from the RSD services list. Each service
should have its own entry in the $apis array and have a unique name, passed as
key for the array that represents the service data. In this data array, the
key-value-pair identified by the apiLink key is required.
&$apis: array of services

'ApiTokensGetTokenTypes': Use this hook to extend action=tokens with new token
types.
&$tokenTypes: supported token types in format 'type' => callback function
used to retrieve this type of tokens.

'Article::MissingArticleConditions': Before fetching deletion & move log entries
to display a message of a non-existing page being deleted/moved, give extensions
a chance to hide their (unrelated) log entries.
&$conds: Array of query conditions (all of which have to be met; conditions will
AND in the final query)
$logTypes: Array of log types being queried

'ArticleAfterFetchContent': After fetching content of an article from the
database. DEPRECATED, use ArticleAfterFetchContentObject instead.
$article: the article (object) being loaded from the database
&$content: the content (string) of the article

'ArticleAfterFetchContentObject': After fetching content of an article from the
database.
$article: the article (object) being loaded from the database
&$content: the content of the article, as a Content object

'ArticleConfirmDelete': Before writing the confirmation form for article
deletion.
$article: the article (object) being deleted
$output: the OutputPage object
&$reason: the reason (string) the article is being deleted

'ArticleContentOnDiff': Before showing the article content below a diff. Use
this to change the content in this area or how it is loaded.
$diffEngine: the DifferenceEngine
$output: the OutputPage object

'ArticleDelete': Before an article is deleted.
$wikiPage: the WikiPage (object) being deleted
$user: the user (object) deleting the article
$reason: the reason (string) the article is being deleted
$error: if the deletion was prohibited, the (raw HTML) error message to display
  (added in 1.13)
$status: Status object, modify this to throw an error. Overridden by $error
  (added in 1.20)

'ArticleDeleteComplete': After an article is deleted.
$wikiPage: the WikiPage that was deleted
$user: the user that deleted the article
$reason: the reason the article was deleted
$id: id of the article that was deleted
$content: the Content of the deleted page
$logEntry: the ManualLogEntry used to record the deletion

'ArticleEditUpdateNewTalk': Before updating user_newtalk when a user talk page
was changed.
&$wikiPage: WikiPage (object) of the user talk page
$recipient: User (object) who's talk page was edited

'ArticleEditUpdates': When edit updates (mainly link tracking) are made when an
article has been changed.
$wikiPage: the WikiPage (object)
$editInfo: data holder that includes the parser output ($editInfo->output) for
that page after the change
$changed: bool for if the page was changed

'ArticleEditUpdatesDeleteFromRecentchanges': Before deleting old entries from
recentchanges table, return false to not delete old entries.
$wikiPage: WikiPage (object) being modified

'ArticleFromTitle': when creating an article object from a title object using
Wiki::articleFromTitle().
$title: Title (object) used to create the article object
$article: Article (object) that will be returned
$context: IContextSource (object)

'ArticleInsertComplete': After a new article is created. DEPRECATED, use
PageContentInsertComplete.
$wikiPage: WikiPage created
$user: User creating the article
$text: New content
$summary: Edit summary/comment
$isMinor: Whether or not the edit was marked as minor
$isWatch: (No longer used)
$section: (No longer used)
$flags: Flags passed to WikiPage::doEditContent()
$revision: New Revision of the article

'ArticleMergeComplete': After merging to article using Special:Mergehistory.
$targetTitle: target title (object)
$destTitle: destination title (object)

'ArticlePageDataAfter': After loading data of an article from the database.
$wikiPage: WikiPage (object) whose data were loaded
$row: row (object) returned from the database server

'ArticlePageDataBefore': Before loading data of an article from the database.
$wikiPage: WikiPage (object) that data will be loaded
$fields: fields (array) to load from the database

'ArticlePrepareTextForEdit': Called when preparing text to be saved.
$wikiPage: the WikiPage being saved
$popts: parser options to be used for pre-save transformation

'ArticleProtect': Before an article is protected.
$wikiPage: the WikiPage being protected
$user: the user doing the protection
$protect: boolean whether this is a protect or an unprotect
$reason: Reason for protect
$moveonly: boolean whether this is for move only or not

'ArticleProtectComplete': After an article is protected.
$wikiPage: the WikiPage that was protected
$user: the user who did the protection
$protect: boolean whether it was a protect or an unprotect
$reason: Reason for protect
$moveonly: boolean whether it was for move only or not

'ArticlePurge': Before executing "&action=purge".
$wikiPage: WikiPage (object) to purge

'ArticleRevisionVisibilitySet': Called when changing visibility of one or more
revisions of an article.
&$title: Title object of the article

'ArticleRevisionUndeleted': After an article revision is restored.
$title: the article title
$revision: the revision
$oldPageID: the page ID of the revision when archived (may be null)

'ArticleRollbackComplete': After an article rollback is completed.
$wikiPage: the WikiPage that was edited
$user: the user who did the rollback
$revision: the revision the page was reverted back to
$current: the reverted revision

'ArticleSave': Before an article is saved. DEPRECATED, use PageContentSave
instead.
$wikiPage: the WikiPage (object) being saved
$user: the user (object) saving the article
$text: the new article text
$summary: the article summary (comment)
$isminor: minor flag
$iswatch: watch flag
$section: section #

'ArticleSaveComplete': After an article has been updated. DEPRECATED, use
PageContentSaveComplete instead.
$wikiPage: WikiPage modified
$user: User performing the modification
$text: New content
$summary: Edit summary/comment
$isMinor: Whether or not the edit was marked as minor
$isWatch: (No longer used)
$section: (No longer used)
$flags: Flags passed to WikiPage::doEditContent()
$revision: New Revision of the article
$status: Status object about to be returned by doEditContent()
$baseRevId: the rev ID (or false) this edit was based on

'ArticleUndelete': When one or more revisions of an article are restored.
$title: Title corresponding to the article restored
$create: Whether or not the restoration caused the page to be created (i.e. it
  didn't exist before).
$comment: The comment associated with the undeletion.
$oldPageId: ID of page previously deleted (from archive table)

'ArticleUndeleteLogEntry': When a log entry is generated but not yet saved.
$pageArchive: the PageArchive object
&$logEntry: ManualLogEntry object
$user: User who is performing the log action

'ArticleUpdateBeforeRedirect': After a page is updated (usually on save), before
the user is redirected back to the page.
&$article: the article
&$sectionanchor: The section anchor link (e.g. "#overview" )
&$extraq: Extra query parameters which can be added via hooked functions

'ArticleViewFooter': After showing the footer section of an ordinary page view
$article: Article object
$patrolFooterShown: boolean whether patrol footer is shown

'ArticleViewHeader': Before the parser cache is about to be tried for article
viewing.
&$article: the article
&$pcache: whether to try the parser cache or not
&$outputDone: whether the output for this page finished or not. Set to a ParserOutput
object to both indicate that the output is done and what parser output was used.

'ArticleViewRedirect': Before setting "Redirected from ..." subtitle when a
redirect was followed.
$article: target article (object)

'ArticleViewCustom': Allows to output the text of the article in a different
format than wikitext. DEPRECATED, use ArticleContentViewCustom instead. Note
that it is preferable to implement proper handing for a custom data type using
the ContentHandler facility.
$text: text of the page
$title: title of the page
$output: reference to $wgOut

'ArticleContentViewCustom': Allows to output the text of the article in a
different format than wikitext. Note that it is preferable to implement proper
handing for a custom data type using the ContentHandler facility.
$content: content of the page, as a Content object
$title: title of the page
$output: reference to $wgOut

'AuthPluginAutoCreate': Called when creating a local account for an user logged
in from an external authentication method.
$user: User object created locally

'AuthPluginSetup': Update or replace authentication plugin object ($wgAuth).
Gives a chance for an extension to set it programmatically to a variable class.
&$auth: the $wgAuth object, probably a stub

'AutopromoteCondition': Check autopromote condition for user.
$type: condition type
$args: arguments
$user: user
$result: result of checking autopromote condition

'BacklinkCacheGetPrefix': Allows to set prefix for a specific link table.
$table: table name
&$prefix: prefix

'BacklinkCacheGetConditions': Allows to set conditions for query when links to
certain title are fetched.
$table: table name
$title: title of the page to which backlinks are sought
&$conds: query conditions

'BadImage': When checking against the bad image list. Change $bad and return
false to override. If an image is "bad", it is not rendered inline in wiki
pages or galleries in category pages.
$name: Image name being checked
&$bad: Whether or not the image is "bad"

'BaseTemplateAfterPortlet': After output of portlets, allow injecting
custom HTML after the section. Any uses of the hook need to handle escaping.
$template BaseTemplate
$portlet: string portlet name
&$html: string

'BeforeDisplayNoArticleText': Before displaying message key "noarticletext" or
"noarticletext-nopermission" at Article::showMissingArticle().
$article: article object

'BeforeInitialize': Before anything is initialized in
MediaWiki::performRequest().
&$title: Title being used for request
$unused: null
&$output: OutputPage object
&$user: User
$request: WebRequest object
$mediaWiki: Mediawiki object

'BeforePageDisplay': Prior to outputting a page.
&$out: OutputPage object
&$skin: Skin object

'BeforeHttpsRedirect': Prior to forcing HTTP->HTTPS redirect. Gives a chance to
override how the redirect is output by modifying, or by returning false, and
letting standard HTTP rendering take place.
ATTENTION: This hook is likely to be removed soon due to overall design of the system.
$context: IContextSource object
&$redirect: string URL, modifiable

'BeforePageRedirect': Prior to sending an HTTP redirect. Gives a chance to
override how the redirect is output by modifying, or by returning false and
taking over the output.
$out: OutputPage object
&$redirect: URL, modifiable
&$code: HTTP code (eg '301' or '302'), modifiable

'BeforeParserFetchFileAndTitle': Before an image is rendered by Parser.
$parser: Parser object
$nt: the image title
&$options: array of options to RepoGroup::findFile
&$descQuery: query string to add to thumbnail URL

FIXME: Where does the below sentence fit in?
If 'broken' is a key in $options then the file will appear as a broken thumbnail.

'BeforeParserFetchTemplateAndtitle': Before a template is fetched by Parser.
$parser: Parser object
$title: title of the template
&$skip: skip this template and link it?
&$id: the id of the revision being parsed

'BeforeParserrenderImageGallery': Before an image gallery is rendered by Parser.
&$parser: Parser object
&$ig: ImageGallery object

'BeforeWelcomeCreation': Before the welcomecreation message is displayed to a
newly created user.
&$welcome_creation_msg: MediaWiki message name to display on the welcome screen
  to a newly created user account.
&$injected_html: Any HTML to inject after the "logged in" message of a newly
  created user account

'BitmapHandlerTransform': before a file is transformed, gives extension the
possibility to transform it themselves
$handler: BitmapHandler
$image: File
&$scalerParams: Array with scaler parameters
&$mto: null, set to a MediaTransformOutput

'BitmapHandlerCheckImageArea': By BitmapHandler::normaliseParams, after all
normalizations have been performed, except for the $wgMaxImageArea check.
$image: File
&$params: Array of parameters
&$checkImageAreaHookResult: null, set to true or false to override the
  $wgMaxImageArea check result.

'PerformRetroactiveAutoblock': Called before a retroactive autoblock is applied
to a user.
$block: Block object (which is set to be autoblocking)
&$blockIds: Array of block IDs of the autoblock

'BlockIp': Before an IP address or user is blocked.
$block: the Block object about to be saved
$user: the user _doing_ the block (not the one being blocked)
&$reason: if the hook is aborted, the error message to be returned in an array

'BlockIpComplete': After an IP address or user is blocked.
$block: the Block object that was saved
$user: the user who did the block (not the one being blocked)

'BookInformation': Before information output on Special:Booksources.
$isbn: ISBN to show information for
$output: OutputPage object in use

'CanIPUseHTTPS': Determine whether the client at a given source IP is likely
to be able to access the wiki via HTTPS.
$ip: The IP address in human-readable form
&$canDo: This reference should be set to false if the client may not be able
to use HTTPS

'CanonicalNamespaces': For extensions adding their own namespaces or altering
the defaults.
Note that if you need to specify namespace protection or content model for
a namespace that is added in a CanonicalNamespaces hook handler, you
should do so by altering $wgNamespaceProtection and
$wgNamespaceContentModels outside the handler, in top-level scope. The
point at which the CanonicalNamespaces hook fires is too late for altering
these variables. This applies even if the namespace addition is
conditional; it is permissible to declare a content model and protection
for a namespace and then decline to actually register it.
&$namespaces: Array of namespace numbers with corresponding canonical names

'CategoryAfterPageAdded': After a page is added to a category.
$category: Category that page was added to
$wikiPage: WikiPage that was added

'CategoryAfterPageRemoved': After a page is removed from a category.
$category: Category that page was removed from
$wikiPage: WikiPage that was removed

'CategoryPageView': Before viewing a categorypage in CategoryPage::view.
$catpage: CategoryPage instance

'ChangePasswordForm': For extensions that need to add a field to the
ChangePassword form via the Preferences form.
&$extraFields: An array of arrays that hold fields like would be passed to the
  pretty function.

'ChangesListInsertArticleLink': Override or augment link to article in RC list.
&$changesList: ChangesList instance.
&$articlelink: HTML of link to article (already filled-in).
&$s: HTML of row that is being constructed.
&$rc: RecentChange instance.
$unpatrolled: Whether or not we are showing unpatrolled changes.
$watched: Whether or not the change is watched by the user.

'ChangesListInitRows': Batch process change list rows prior to rendering.
$changesList: ChangesList instance
$rows: The data that will be rendered. May be a ResultWrapper instance or
  an array.

'ChangesListSpecialPageFilters': Called after building form options on pages inheriting from ChangesListSpecialPage (in core: RecentChanges, RecentChangesLinked and Watchlist).
$special: ChangesListSpecialPage instance
&$filters: associative array of filter definitions. The keys are the HTML
  name/URL parameters. Each key maps to an associative array with a 'msg'
  (message key) and a 'default' value.

'ChangesListSpecialPageQuery': Called when building SQL query on pages inheriting from ChangesListSpecialPage (in core: RecentChanges, RecentChangesLinked and Watchlist).
$name: name of the special page, e.g. 'Watchlist'
&$tables: array of tables to be queried
&$fields: array of columns to select
&$conds: array of WHERE conditionals for query
&$query_options: array of options for the database request
&$join_conds: join conditions for the tables
$opts: FormOptions for this request

'Collation::factory': Called if $wgCategoryCollation is an unknown collation.
$collationName: Name of the collation in question
&$collationObject: Null. Replace with a subclass of the Collation class that
  implements the collation given in $collationName.

'ConfirmEmailComplete': Called after a user's email has been confirmed
successfully.
$user: user (object) whose email is being confirmed

'ContentHandlerDefaultModelFor': Called when the default content model is determined
for a given title. May be used to assign a different model for that title.
$title: the Title in question
&$model: the model name. Use with CONTENT_MODEL_XXX constants.

'ContentHandlerForModelID': Called when a ContentHandler is requested for a given
content model name, but no entry for that model exists in $wgContentHandlers.
$modeName: the requested content model name
&$handler: set this to a ContentHandler object, if desired.

'ContentModelCanBeUsedOn': Called to determine whether that content model can
be used on a given page. This is especially useful to prevent some content models
to be used in some special location.
$contentModel: ID of the content model in question
$title: the Title in question.
&$ok: Output parameter, whether it is OK to use $contentModel on $title.
Handler functions that modify $ok should generally return false to prevent further
hooks from further modifying $ok.

'ContentGetParserOutput': Customize parser output for a given content object,
called by AbstractContent::getParserOutput. May be used to override the normal
model-specific rendering of page content.
$content: The Content to render
$title: Title of the page, as context
$revId: The revision ID, as context
$options: ParserOptions for rendering. To avoid confusing the parser cache,
the output can only depend on parameters provided to this hook function, not on global state.
$generateHtml: boolean, indicating whether full HTML should be generated. If false,
generation of HTML may be skipped, but other information should still be present in the
ParserOutput object.
&$output: ParserOutput, to manipulate or replace

'ConvertContent': Called by AbstractContent::convert when a conversion to another
content model is requested.
$content: The Content object to be converted.
$toModel: The ID of the content model to convert to.
$lossy:   boolean indicating whether lossy conversion is allowed.
&$result: Output parameter, in case the handler function wants to provide a
converted Content object. Note that $result->getContentModel() must return $toModel.
Handler functions that modify $result should generally return false to further
attempts at conversion.

'ContribsPager::getQueryInfo': Before the contributions query is about to run
&$pager: Pager object for contributions
&$queryInfo: The query for the contribs Pager

'ContribsPager::reallyDoQuery': Called before really executing the query for My Contributions
&$data: an array of results of all contribs queries
$pager: The ContribsPager object hooked into
$offset: Index offset, inclusive
$limit: Exact query limit
$descending: Query direction, false for ascending, true for descending

'ContributionsLineEnding': Called before a contributions HTML line is finished
$page: SpecialPage object for contributions
&$ret: the HTML line
$row: the DB row for this line
&$classes: the classes to add to the surrounding <li>

'ContributionsToolLinks': Change tool links above Special:Contributions
$id: User identifier
$title: User page title
&$tools: Array of tool links

'CustomEditor': When invoking the page editor
$article: Article being edited
$user: User performing the edit

Return true to allow the normal editor to be used, or false
if implementing a custom editor, e.g. for a special namespace,
etc.

'DatabaseOraclePostInit': Called after initialising an Oracle database
&$db: the DatabaseOracle object

'NewDifferenceEngine': Called when a new DifferenceEngine object is made
$title: the diff page title (nullable)
&$oldId: the actual old Id to use in the diff
&$newId: the actual new Id to use in the diff (0 means current)
$old: the ?old= param value from the url
$new: the ?new= param value from the url

'DiffRevisionTools': Override or extend the revision tools available from the
diff view, i.e. undo, etc.
$newRev: Revision object of the "new" revision
&$links: Array of HTML links
$oldRev: Revision object of the "old" revision (may be null)

'DiffViewHeader': Called before diff display
$diff: DifferenceEngine object that's calling
$oldRev: Revision object of the "old" revision (may be null/invalid)
$newRev: Revision object of the "new" revision

'DisplayOldSubtitle': before creating subtitle when browsing old versions of
an article
$article: article (object) being viewed
$oldid: oldid (int) being viewed

'DoEditSectionLink': Override the HTML generated for section edit links
$skin: Skin object rendering the UI
$title: Title object for the title being linked to (may not be the same as
  the page title, if the section is included from a template)
$section: The designation of the section being pointed to, to be included in
  the link, like "&section=$section"
$tooltip: The default tooltip.  Escape before using.
  By default, this is wrapped in the 'editsectionhint' message.
&$result: The HTML to return, prefilled with the default plus whatever other
  changes earlier hooks have made
$lang: The language code to use for the link in the wfMessage function

'EditFilter': Perform checks on an edit
$editor: EditPage instance (object). The edit form (see includes/EditPage.php)
$text: Contents of the edit box
$section: Section being edited
&$error: Error message to return
$summary: Edit summary for page

'EditFilterMerged': Post-section-merge edit filter.
DEPRECATED, use EditFilterMergedContent instead.
$editor: EditPage instance (object)
$text: content of the edit box
&$error: error message to return
$summary: Edit summary for page

'EditFilterMergedContent': Post-section-merge edit filter.
This may be triggered by the EditPage or any other facility that modifies page content.
Use the $status object to indicate whether the edit should be allowed, and to provide
a reason for disallowing it. Return false to abort the edit, and true to continue.
Returning true if $status->isOK() returns false means "don't save but continue user
interaction", e.g. show the edit form.
$context: object implementing the IContextSource interface.
$content: content of the edit box, as a Content object.
$status: Status object to represent errors, etc.
$summary: Edit summary for page
$user: the User object representing the user whois performing the edit.
$minoredit: whether the edit was marked as minor by the user.

'EditFormPreloadText': Allows population of the edit form when creating
new pages
&$text: Text to preload with
&$title: Title object representing the page being created

'EditFormInitialText': Allows modifying the edit form when editing existing
pages
$editPage: EditPage     object

'EditPage::attemptSave': Called before an article is
saved, that is before WikiPage::doEditContent() is called
$editpage_Obj: the current EditPage object

'EditPage::importFormData': allow extensions to read additional data
posted in the form
$editpage: EditPage instance
$request: Webrequest
return value is ignored (should always return true)

'EditPage::showEditForm:fields': allows injection of form field into edit form
$editor: the EditPage instance for reference
$out: an OutputPage instance to write to
return value is ignored (should always return true)

'EditPage::showEditForm:initial': before showing the edit form
$editor: EditPage instance (object)
$out: an OutputPage instance to write to

Return false to halt editing; you'll need to handle error messages, etc.
yourself. Alternatively, modifying $error and returning true will cause the
contents of $error to be echoed at the top of the edit form as wikitext.
Return true without altering $error to allow the edit to proceed.

'EditPage::showReadOnlyForm:initial': similar to EditPage::showEditForm:initial
but for the read-only 'view source' variant of the edit form.
$editor: EditPage instance (object)
&$out: an OutputPage instance to write to
return value is ignored (should always return true)

'EditPage::showStandardInputs:options': allows injection of form fields into
the editOptions area
$editor: EditPage instance (object)
$out: an OutputPage instance to write to
&$tabindex: HTML tabindex of the last edit check/button
return value is ignored (should always be true)

'EditPageBeforeConflictDiff': allows modifying the EditPage object and output
when there's an edit conflict.  Return false to halt normal diff output; in
this case you're responsible for computing and outputting the entire "conflict"
part, i.e., the "difference between revisions" and "your text" headers and
sections.
&$editor: EditPage instance
&$out: OutputPage instance

'EditPageBeforeEditButtons': Allows modifying the edit buttons below the
textarea in the edit form.
&$editpage: The current EditPage object
&$buttons: Array of edit buttons "Save", "Preview", "Live", and "Diff"
&$tabindex: HTML tabindex of the last edit check/button

'EditPageBeforeEditChecks': Allows modifying the edit checks below the textarea
in the edit form.
&$editpage: The current EditPage object
&$checks: Array of edit checks like "watch this page"/"minor edit"
&$tabindex: HTML tabindex of the last edit check/button

'EditPageBeforeEditToolbar': Allows modifying the edit toolbar above the
textarea in the edit form.
&$toolbar: The toolbar HTMl

'EditPageCopyrightWarning': Allow for site and per-namespace customization of
contribution/copyright notice.
$title: title of page being edited
&$msg: localization message name, overridable. Default is either
  'copyrightwarning' or 'copyrightwarning2'.

'EditPageGetDiffText': DEPRECATED. Use EditPageGetDiffContent instead. Allow
modifying the wikitext that will be used in "Show changes". Note that it is
preferable to implement diff handling for different data types using the
ContentHandler facility.
$editPage: EditPage object
&$newtext: wikitext that will be used as "your version"

'EditPageGetDiffContent': Allow modifying the wikitext that will be used in
"Show changes". Note that it is preferable to implement diff handling for
different data types using the ContentHandler facility.
$editPage: EditPage object
&$newtext: wikitext that will be used as "your version"

'EditPageGetPreviewText': DEPRECATED. Use EditPageGetPreviewContent instead.
Allow modifying the wikitext that will be previewed. Note that it is preferable
to implement previews for different data types using the ContentHandler
facility.
$editPage: EditPage object
&$toparse: wikitext that will be parsed

'EditPageGetPreviewContent': Allow modifying the wikitext that will be
previewed. Note that it is preferable to implement previews for different data
types using the ContentHandler facility.
$editPage: EditPage object
&$content: Content object to be previewed (may be replaced by hook function)

'EditPageNoSuchSection': When a section edit request is given for an non-existent section
&$editpage: The current EditPage object
&$res: the HTML of the error text

'EditPageTosSummary': Give a chance for site and per-namespace customizations
of terms of service summary link that might exist separately from the copyright
notice.
$title: title of page being edited
&$msg: localization message name, overridable. Default is 'editpage-tos-summary'

'EmailConfirmed': When checking that the user's email address is "confirmed".
$user: User being checked
$confirmed: Whether or not the email address is confirmed
This runs before the other checks, such as anonymity and the real check; return
true to allow those checks to occur, and false if checking is done.

'EmailUser': Before sending email from one user to another.
$to: address of receiving user
$from: address of sending user
$subject: subject of the mail
$text: text of the mail

'EmailUserCC': Before sending the copy of the email to the author.
$to: address of receiving user
$from: address of sending user
$subject: subject of the mail
$text: text of the mail

'EmailUserComplete': After sending email from one user to another.
$to: address of receiving user
$from: address of sending user
$subject: subject of the mail
$text: text of the mail

'EmailUserForm': After building the email user form object.
$form: HTMLForm object

'EmailUserPermissionsErrors': to retrieve permissions errors for emailing a
user.
$user: The user who is trying to email another user.
$editToken: The user's edit token.
&$hookErr: Out-param for the error. Passed as the parameters to
  OutputPage::showErrorPage.

'ExemptFromAccountCreationThrottle': Exemption from the account creation
throttle.
$ip: The ip address of the user

'ExtensionTypes': Called when generating the extensions credits, use this to
change the tables headers.
&$extTypes: associative array of extensions types

'ExtractThumbParameters': Called when extracting thumbnail parameters from a
thumbnail file name.
DEPRECATED: Media handler should override MediaHandler::parseParamString instead.
$thumbname: the base name of the thumbnail file
&$params: the currently extracted params (has source name, temp or archived zone)

'FetchChangesList': When fetching the ChangesList derivative for a particular
user.
$user: User the list is being fetched for
&$skin: Skin object to be used with the list
&$list: List object (defaults to NULL, change it to an object instance and
  return false override the list derivative used)

'FileDeleteComplete': When a file is deleted.
$file: reference to the deleted file
$oldimage: in case of the deletion of an old image, the name of the old file
$article: in case all revisions of the file are deleted a reference to the
  WikiFilePage associated with the file.
$user: user who performed the deletion
$reason: reason

'FileTransformed': When a file is transformed and moved into storage.
$file: reference to the File object
$thumb: the MediaTransformOutput object
$tmpThumbPath: The temporary file system path of the transformed file
$thumbPath: The permanent storage path of the transformed file

'FileUpload': When a file upload occurs.
$file : Image object representing the file that was uploaded
$reupload : Boolean indicating if there was a previously another image there or
  not (since 1.17)
$hasDescription : Boolean indicating that there was already a description page
  and a new one from the comment wasn't created (since 1.17)

'FileUndeleteComplete': When a file is undeleted
$title: title object to the file
$fileVersions: array of undeleted versions. Empty if all versions were restored
$user: user who performed the undeletion
$reason: reason

'FormatAutocomments': When an autocomment is formatted by the Linker.
 &$comment: Reference to the accumulated comment. Initially null, when set the
   default code will be skipped.
 $pre: Initial part of the parsed comment before the call to the hook.
 $auto: The extracted part of the parsed comment before the call to the hook.
 $post: The final part of the parsed comment before the call to the hook.
 $title: An optional title object used to links to sections. Can be null.
 $local: Boolean indicating whether section links should refer to local page.

'GalleryGetModes': Get list of classes that can render different modes of a
 gallery
$modeArray: An associative array mapping mode names to classes that implement
 that mode. It is expected all registered classes are a subclass of
 ImageGalleryBase.

'GetAutoPromoteGroups': When determining which autopromote groups a user is
entitled to be in.
&$user: user to promote.
&$promote: groups that will be added.

'GetBlockedStatus': after loading blocking status of an user from the database
$user: user (object) being checked

'GetCacheVaryCookies': Get cookies that should vary cache options.
$out: OutputPage object
&$cookies: array of cookies name, add a value to it if you want to add a cookie
  that have to vary cache options

'GetCanonicalURL': Modify fully-qualified URLs used for IRC and e-mail
notifications.
$title: Title object of page
$url: string value as output (out parameter, can modify)
$query: query options passed to Title::getCanonicalURL()

'GetDefaultSortkey': Override the default sortkey for a page.
$title: Title object that we need to get a sortkey for
&$sortkey: Sortkey to use.

'GetDoubleUnderscoreIDs': Modify the list of behavior switch (double
underscore) magic words. Called by MagicWord.
&$doubleUnderscoreIDs: array of strings

'GetExtendedMetadata': Get extended file metadata for the API
&$combinedMeta: Array of the form: 'MetadataPropName' => array(
'value' => prop value, 'source' => 'name of hook' ).
$file: File object of file in question
$context: RequestContext (including language to use)
$single: Only extract the current language; if false, the prop value should
be in the metadata multi-language array format:
mediawiki.org/wiki/Manual:File_metadata_handling#Multi-language_array_format
&$maxCacheTime: how long the results can be cached

'GetFullURL': Modify fully-qualified URLs used in redirects/export/offsite data.
$title: Title object of page
$url: string value as output (out parameter, can modify)
$query: query options passed to Title::getFullURL()

'GetHumanTimestamp': Pre-emptively override the human-readable timestamp generated
by MWTimestamp::getHumanTimestamp(). Return false in this hook to use the custom
output.
&$output: string for the output timestamp
$timestamp: MWTimestamp object of the current (user-adjusted) timestamp
$relativeTo: MWTimestamp object of the relative (user-adjusted) timestamp
$user: User whose preferences are being used to make timestamp
$lang: Language that will be used to render the timestamp

'GetInternalURL': Modify fully-qualified URLs used for squid cache purging.
$title: Title object of page
$url: string value as output (out parameter, can modify)
$query: query options passed to Title::getInternalURL()

'GetIP': modify the ip of the current user (called only once).
&$ip: string holding the ip as determined so far

'GetLinkColours': modify the CSS class of an array of page links.
$linkcolour_ids: array of prefixed DB keys of the pages linked to,
        indexed by page_id.
&$colours: (output) array of CSS classes, indexed by prefixed DB keys

'GetLocalURL': Modify local URLs as output into page links. Note that if you are
working with internal urls (non-interwiki) then it may be preferable to work
with the GetLocalURL::Internal or GetLocalURL::Article hooks as GetLocalURL can
be buggy for internal urls on render if you do not re-implement the horrible
hack that Title::getLocalURL uses in your own extension.
$title: Title object of page
&$url: string value as output (out parameter, can modify)
$query: query options passed to Title::getLocalURL()

'GetLocalURL::Internal': Modify local URLs to internal pages.
$title: Title object of page
&$url: string value as output (out parameter, can modify)
$query: query options passed to Title::getLocalURL()

'GetLocalURL::Article': Modify local URLs specifically pointing to article paths
without any fancy queries or variants.
$title: Title object of page
&$url: string value as output (out parameter, can modify)

'GetLogTypesOnUser': Add log types where the target is a userpage
&$types: Array of log types

'GetMetadataVersion': Modify the image metadata version currently in use. This
is used when requesting image metadata from a ForeignApiRepo. Media handlers
that need to have versioned metadata should add an element to the end of the
version array of the form 'handler_name=version'. Most media handlers won't need
to do this unless they broke backwards compatibility with a previous version of
the media handler metadata output.
&$version: Array of version strings

'GetNewMessagesAlert': Disable or modify the new messages alert
&$newMessagesAlert: An empty string by default. If the user has new talk page
messages, this should be populated with an alert message to that effect
$newtalks: An empty array if the user has no new messages or an array containing
links and revisions if there are new messages (See User::getNewMessageLinks)
$user: The user object of the user who is loading the page
$out: OutputPage object (to check what type of page the user is on)

'GetPreferences': Modify user preferences.
$user: User whose preferences are being modified.
&$preferences: Preferences description array, to be fed to an HTMLForm object

'GetRelativeTimestamp': Pre-emptively override the relative timestamp generated
by MWTimestamp::getRelativeTimestamp(). Return false in this hook to use the custom
output.
&$output: string for the output timestamp
&$diff: DateInterval representing the difference between the timestamps
$timestamp: MWTimestamp object of the current (user-adjusted) timestamp
$relativeTo: MWTimestamp object of the relative (user-adjusted) timestamp
$user: User whose preferences are being used to make timestamp
$lang: Language that will be used to render the timestamp

'getUserPermissionsErrors': Add a permissions error when permissions errors are
checked for. Use instead of userCan for most cases. Return false if the user
can't do it, and populate $result with the reason in the form of
array( messagename, param1, param2, ... ). For consistency, error messages
should be plain text with no special coloring, bolding, etc. to show that
they're errors; presenting them properly to the user as errors is done by the
caller.
$title: Title object being checked against
$user : Current user object
$action: Action being checked
$result: User permissions error to add. If none, return true.

'getUserPermissionsErrorsExpensive': Equal to getUserPermissionsErrors, but is
called only if expensive checks are enabled. Add a permissions error when
permissions errors are checked for. Return false if the user can't do it, and
populate $result with the reason in the form of array( messagename, param1,
param2, ... ). For consistency, error messages should be plain text with no
special coloring, bolding, etc. to show that they're errors; presenting them
properly to the user as errors is done by the caller.

$title: Title object being checked against
$user : Current user object
$action: Action being checked
$result: User permissions error to add. If none, return true.

'GitViewers': Called when generating the list of git viewers for
Special:Version, use this to change the list.
&$extTypes: associative array of repo URLS to viewer URLs.

'HistoryRevisionTools': Override or extend the revision tools available from the
page history view, i.e. undo, rollback, etc.
$rev: Revision object
&$links: Array of HTML links

'ImageBeforeProduceHTML': Called before producing the HTML created by a wiki
image insertion. You can skip the default logic entirely by returning false, or
just modify a few things using call-by-reference.
&$skin: Skin object
&$title: Title object of the image
&$file: File object, or false if it doesn't exist
&$frameParams: Various parameters with special meanings; see documentation in
  includes/Linker.php for Linker::makeImageLink
&$handlerParams: Various parameters with special meanings; see documentation in
  includes/Linker.php for Linker::makeImageLink
&$time: Timestamp of file in 'YYYYMMDDHHIISS' string form, or false for current
&$res: Final HTML output, used if you return false


'ImageOpenShowImageInlineBefore': Call potential extension just before showing
the image on an image page.
$imagePage: ImagePage object ($this)
$output: $wgOut

'ImagePageAfterImageLinks': Called after the image links section on an image
page is built.
$imagePage: ImagePage object ($this)
&$html: HTML for the hook to add

'ImagePageFileHistoryLine': Called when a file history line is constructed.
$file: the file
$line: the HTML of the history line
$css: the line CSS class

'ImagePageFindFile': Called when fetching the file associated with an image
page.
$page: ImagePage object
&$file: File object
&$displayFile: displayed File object

'ImagePageShowTOC': Called when the file toc on an image page is generated.
$page: ImagePage object
&$toc: Array of <li> strings

'ImgAuthBeforeStream': executed before file is streamed to user, but only when
using img_auth.php.
&$title: the Title object of the file as it would appear for the upload page
&$path: the original file and path name when img_auth was invoked by the the web
  server
&$name: the name only component of the file
&$result: The location to pass back results of the hook routine (only used if
  failed)
  $result[0]=The index of the header message
  $result[1]=The index of the body text message
  $result[2 through n]=Parameters passed to body text message. Please note the
  header message cannot receive/use parameters.

'ImportHandleLogItemXMLTag': When parsing a XML tag in a log item.
$reader: XMLReader object
$logInfo: Array of information
Return false to stop further processing of the tag

'ImportHandlePageXMLTag': When parsing a XML tag in a page.
$reader: XMLReader object
$pageInfo: Array of information
Return false to stop further processing of the tag

'ImportHandleRevisionXMLTag': When parsing a XML tag in a page revision.
$reader: XMLReader object
$pageInfo: Array of page information
$revisionInfo: Array of revision information
Return false to stop further processing of the tag

'ImportHandleToplevelXMLTag': When parsing a top level XML tag.
$reader: XMLReader object
Return false to stop further processing of the tag

'ImportHandleUploadXMLTag': When parsing a XML tag in a file upload.
$reader: XMLReader object
$revisionInfo: Array of information
Return false to stop further processing of the tag

'InfoAction': When building information to display on the action=info page.
$context: IContextSource object
&$pageInfo: Array of information

'InitializeArticleMaybeRedirect': MediaWiki check to see if title is a redirect.
$title: Title object for the current page
$request: WebRequest
$ignoreRedirect: boolean to skip redirect check
$target: Title/string of redirect target
$article: Article object

'InterwikiLoadPrefix': When resolving if a given prefix is an interwiki or not.
Return true without providing an interwiki to continue interwiki search.
$prefix: interwiki prefix we are looking for.
&$iwData: output array describing the interwiki with keys iw_url, iw_local,
  iw_trans and optionally iw_api and iw_wikiid.

'InternalParseBeforeSanitize': during Parser's internalParse method just before
the parser removes unwanted/dangerous HTML tags and after nowiki/noinclude/
includeonly/onlyinclude and other processings. Ideal for syntax-extensions after
template/parser function execution which respect nowiki and HTML-comments.
&$parser: Parser object
&$text: string containing partially parsed text
&$stripState: Parser's internal StripState object

'InternalParseBeforeLinks': during Parser's internalParse method before links
but after nowiki/noinclude/includeonly/onlyinclude and other processings.
&$parser: Parser object
&$text: string containing partially parsed text
&$stripState: Parser's internal StripState object

'InvalidateEmailComplete': Called after a user's email has been invalidated
successfully.
$user: user (object) whose email is being invalidated

'IRCLineURL': When constructing the URL to use in an IRC notification.
Callee may modify $url and $query, URL will be constructed as $url . $query
&$url: URL to index.php
&$query: Query string
$rc: RecentChange object that triggered url generation

'IsFileCacheable': Override the result of Article::isFileCacheable() (if true)
$article: article (object) being checked

'IsTrustedProxy': Override the result of wfIsTrustedProxy()
$ip: IP being check
$result: Change this value to override the result of wfIsTrustedProxy()

'IsUploadAllowedFromUrl': Override the result of UploadFromUrl::isAllowedUrl()
$url: URL used to upload from
&$allowed: Boolean indicating if uploading is allowed for given URL

'isValidEmailAddr': Override the result of Sanitizer::validateEmail(), for
instance to return false if the domain name doesn't match your organization.
$addr: The e-mail address entered by the user
&$result: Set this and return false to override the internal checks

'isValidPassword': Override the result of User::isValidPassword()
$password: The password entered by the user
&$result: Set this and return false to override the internal checks
$user: User the password is being validated for

'Language::getMessagesFileName':
$code: The language code or the language we're looking for a messages file for
&$file: The messages file path, you can override this to change the location.

'LanguageGetNamespaces': Provide custom ordering for namespaces or
remove namespaces. Do not use this hook to add namespaces. Use
CanonicalNamespaces for that.
&$namespaces: Array of namespaces indexed by their numbers

'LanguageGetMagic': DEPRECATED, use $magicWords in a file listed in
$wgExtensionMessagesFiles instead.
Use this to define synonyms of magic words depending of the language
$magicExtensions: associative array of magic words synonyms
$lang: language code (string)

'LanguageGetSpecialPageAliases': DEPRECATED, use $specialPageAliases in a file
listed in $wgExtensionMessagesFiles instead.
Use to define aliases of special pages names depending of the language
$specialPageAliases: associative array of magic words synonyms
$lang: language code (string)

'LanguageGetTranslatedLanguageNames': Provide translated language names.
&$names: array of language code => language name
$code language of the preferred translations

'LanguageLinks': Manipulate a page's language links. This is called
in various places to allow extensions to define the effective language
links for a page.
$title: The page's Title.
&$links: Associative array mapping language codes to prefixed links of the
  form "language:title".
&$linkFlags: Associative array mapping prefixed links to arrays of flags.
  Currently unused, but planned to provide support for marking individual
  language links in the UI, e.g. for featured articles.

'LinkBegin': Used when generating internal and interwiki links in
Linker::link(), before processing starts.  Return false to skip default
processing and return $ret. See documentation for Linker::link() for details on
the expected meanings of parameters.
$skin: the Skin object
$target: the Title that the link is pointing to
&$html: the contents that the <a> tag should have (raw HTML); null means
  "default".
&$customAttribs: the HTML attributes that the <a> tag should have, in
associative array form, with keys and values unescaped.  Should be merged with
default values, with a value of false meaning to suppress the attribute.
&$query: the query string to add to the generated URL (the bit after the "?"),
  in associative array form, with keys and values unescaped.
&$options: array of options.  Can include 'known', 'broken', 'noclasses'.
&$ret: the value to return if your hook returns false.

'LinkEnd': Used when generating internal and interwiki links in Linker::link(),
just before the function returns a value.  If you return true, an <a> element
with HTML attributes $attribs and contents $html will be returned.  If you
return false, $ret will be returned.
$skin: the Skin object
$target: the Title object that the link is pointing to
$options: the options.  Will always include either 'known' or 'broken', and may
  include 'noclasses'.
&$html: the final (raw HTML) contents of the <a> tag, after processing.
&$attribs: the final HTML attributes of the <a> tag, after processing, in
  associative array form.
&$ret: the value to return if your hook returns false.

'LinkerMakeExternalImage': At the end of Linker::makeExternalImage() just
before the return.
&$url: the image url
&$alt: the image's alt text
&$img: the new image HTML (if returning false)

'LinkerMakeExternalLink': At the end of Linker::makeExternalLink() just
before the return.
&$url: the link url
&$text: the link text
&$link: the new link HTML (if returning false)
&$attribs: the attributes to be applied.
$linkType: The external link type

'LinkerMakeMediaLinkFile': At the end of Linker::makeMediaLinkFile() just
before the return.
$title: the Title object that the link is pointing to
$file: the File object or false if broken link
&$html: the link text
&$attribs: the attributes to be applied
&$ret: the value to return if your hook returns false

'LinksUpdate': At the beginning of LinksUpdate::doUpdate() just before the
actual update.
&$linksUpdate: the LinksUpdate object

'LinksUpdateAfterInsert': At the end of LinksUpdate::incrTableUpdate() after
each link table insert.  For example, pagelinks, imagelinks, externallinks.
$linksUpdate: LinksUpdate object
$table: the table to insert links to
$insertions: an array of links to insert

'LinksUpdateComplete': At the end of LinksUpdate::doUpdate() when updating,
including delete and insert, has completed for all link tables
&$linksUpdate: the LinksUpdate object

'LinksUpdateConstructed': At the end of LinksUpdate() is construction.
&$linksUpdate: the LinksUpdate object

'ListDefinedTags': When trying to find all defined tags.
&$tags: The list of tags.

'LoadExtensionSchemaUpdates': Called during database installation and updates.
&updater: A DatabaseUpdater subclass

'LocalFile::getHistory': Called before file history query performed.
$file: the File object
$tables: tables
$fields: select fields
$conds: conditions
$opts: query options
$join_conds: JOIN conditions

'LocalFilePurgeThumbnails': Called before thumbnails for a local file a purged.
$file: the File object
$archiveName: name of an old file version or false if it's the current one

'LocalisationCacheRecache': Called when loading the localisation data into
cache.
$cache: The LocalisationCache object
$code: language code
&$alldata: The localisation data from core and extensions
&purgeBlobs: whether to purge/update the message blobs via MessageBlobStore::clear()

'LocalisationChecksBlacklist': When fetching the blacklist of
localisation checks.
&$blacklist: array of checks to blacklist. See the bottom of
  maintenance/language/checkLanguage.inc for the format of this variable.

'LocalisationIgnoredOptionalMessages': When fetching the list of ignored and
optional localisation messages
&$ignored Array of ignored message keys
&$optional Array of optional message keys

'LogEventsListShowLogExtract': Called before the string is added to OutputPage.
Returning false will prevent the string from being added to the OutputPage.
&$s: html string to show for the log extract
$types: String or Array Log types to show
$page: String or Title The page title to show log entries for
$user: String The user who made the log entries
$param: Associative Array with the following additional options:
  - lim Integer Limit of items to show, default is 50
  - conds Array Extra conditions for the query (e.g. "log_action != 'revision'")
  - showIfEmpty boolean Set to false if you don't want any output in case the
    loglist is empty if set to true (default), "No matching items in log" is
    displayed if loglist is empty
  - msgKey Array If you want a nice box with a message, set this to the key of
    the message. First element is the message key, additional optional elements
    are parameters for the key that are processed with
    wfMessage()->params()->parseAsBlock()
  - offset Set to overwrite offset parameter in $wgRequest set to '' to unset
    offset
  - wrap String Wrap the message in html (usually something like
    "&lt;div ...>$1&lt;/div>").
  - flags Integer display flags (NO_ACTION_LINK,NO_EXTRA_USER_LINKS)

'LoginAuthenticateAudit': A login attempt for a valid user account either
succeeded or failed. No return data is accepted; this hook is for auditing only.
$user: the User object being authenticated against
$password: the password being submitted and found wanting
$retval: a LoginForm class constant with authenticateUserData() return
  value (SUCCESS, WRONG_PASS, etc.).

'LoginPasswordResetMessage': User is being requested to reset their password on login.
Use this hook to change the Message that will be output on Special:ChangePassword.
&$msg: Message object that will be shown to the user
$username: Username of the user who's password was expired.

'LogLine': Processes a single log entry on Special:Log.
$log_type: string for the type of log entry (e.g. 'move'). Corresponds to
  logging.log_type database field.
$log_action: string for the type of log action (e.g. 'delete', 'block',
  'create2'). Corresponds to logging.log_action database field.
$title: Title object that corresponds to logging.log_namespace and
  logging.log_title database fields.
$paramArray: Array of parameters that corresponds to logging.log_params field.
  Note that only $paramArray[0] appears to contain anything.
&$comment: string that corresponds to logging.log_comment database field, and
  which is displayed in the UI.
&$revert: string that is displayed in the UI, similar to $comment.
$time: timestamp of the log entry (added in 1.12)

'LonelyPagesQuery': Allow extensions to modify the query used by
Special:LonelyPages.
&$tables: tables to join in the query
&$conds: conditions for the query
&$joinConds: join conditions for the query

'MaintenanceRefreshLinksInit': before executing the refreshLinks.php maintenance
script.
$refreshLinks: RefreshLinks object

'MagicWordwgVariableIDs': When defining new magic words IDs.
$variableIDs: array of strings

'MakeGlobalVariablesScript': Called at end of OutputPage::getJSVars.
Ideally, this hook should only be used to add variables that depend on
the current page/request; static configuration should be added through
ResourceLoaderGetConfigVars instead.
&$vars: variable (or multiple variables) to be added into the output of
  Skin::makeVariablesScript
$out: The OutputPage which called the hook, can be used to get the real title.

'MarkPatrolled': Before an edit is marked patrolled.
$rcid: ID of the revision to be marked patrolled
$user: the user (object) marking the revision as patrolled
$wcOnlySysopsCanPatrol: config setting indicating whether the user needs to be a
  sysop in order to mark an edit patrolled.

'MarkPatrolledComplete': After an edit is marked patrolled.
$rcid: ID of the revision marked as patrolled
$user: user (object) who marked the edit patrolled
$wcOnlySysopsCanPatrol: config setting indicating whether the user must be a
  sysop to patrol the edit.

'MediaWikiPerformAction': Override MediaWiki::performAction(). Use this to do
something completely different, after the basic globals have been set up, but
before ordinary actions take place.
$output: $wgOut
$article: Article on which the action will be performed
$title: Title on which the action will be performed
$user: $wgUser
$request: $wgRequest
$mediaWiki: The $mediawiki object

'MessagesPreLoad': When loading a message from the database.
$title: title of the message (string)
$message: value (string), change it to the message you want to define

'MessageCache::get': When fetching a message. Can be used to override the key
for customisations. Given and returned message key must be in special format:
1) first letter must be in lower case according to the content language.
2) spaces must be replaced with underscores
&$key: message key (string)

'MessageCacheReplace': When a message page is changed. Useful for updating
caches.
$title: name of the page changed.
$text: new contents of the page.

'MimeMagicInit': Before processing the list mapping MIME types to media types
and the list mapping MIME types to file extensions.
As an extension author, you are encouraged to submit patches to MediaWiki's
core to add new MIME types to mime.types.
$mimeMagic: Instance of MimeMagic.
  Use $mimeMagic->addExtraInfo( $stringOfInfo );
  for adding new MIME info to the list.
  Use $mimeMagic->addExtraTypes( $stringOfTypes );
  for adding new MIME types to the list.

'MimeMagicImproveFromExtension': Allows MW extensions to further improve the
MIME type detected by considering the file extension.
$mimeMagic: Instance of MimeMagic.
$ext: File extension.
&$mime: MIME type (in/out).

'MimeMagicGuessFromContent': Allows MW extensions guess the MIME by content.
$mimeMagic: Instance of MimeMagic.
&$head: First 1024 bytes of the file in a string (in - Do not alter!).
&$tail: More or equal than last 65558 bytes of the file in a string
  (in - Do not alter!).
$file: File path.
&$mime: MIME type (out).

'ModifyExportQuery': Modify the query used by the exporter.
$db: The database object to be queried.
&$tables: Tables in the query.
&$conds: Conditions in the query.
&$opts: Options for the query.
&$join_conds: Join conditions for the query.

'MonoBookTemplateToolboxEnd': DEPRECATED. Called by Monobook skin after toolbox
links have been rendered (useful for adding more). Note: this is only run for
the Monobook skin. To add items to the toolbox you should use the
SkinTemplateToolboxEnd hook instead, which works for all "SkinTemplate"-type
skins.
$tools: array of tools

'BaseTemplateToolbox': Called by BaseTemplate when building the $toolbox array
and returning it for the skin to output. You can add items to the toolbox while
still letting the skin make final decisions on skin-specific markup conventions
using this hook.
&$sk: The BaseTemplate base skin template
&$toolbox: An array of toolbox items, see BaseTemplate::getToolbox and
  BaseTemplate::makeListItem for details on the format of individual items
  inside of this array.

'NamespaceIsMovable': Called when determining if it is possible to pages in a
namespace.
$index: Integer; the index of the namespace being checked.
$result: Boolean; whether MediaWiki currently thinks that pages in this
  namespace are movable. Hooks may change this value to override the return
  value of MWNamespace::isMovable().

'NewRevisionFromEditComplete': Called when a revision was inserted due to an
edit.
$wikiPage: the WikiPage edited
$rev: the new revision
$baseID: the revision ID this was based off, if any
$user: the editing user

'NormalizeMessageKey': Called before the software gets the text of a message
(stuff in the MediaWiki: namespace), useful for changing WHAT message gets
displayed.
&$key: the message being looked up. Change this to something else to change
  what message gets displayed (string)
&$useDB: whether or not to look up the message in the database (bool)
&$langCode: the language code to get the message for (string) - or -
  whether to use the content language (true) or site language (false) (bool)
&$transform: whether or not to expand variables and templates
  in the message (bool)

'OldChangesListRecentChangesLine': Customize entire recent changes line, or
return false to omit the line from RecentChanges and Watchlist special pages.
&$changeslist: The OldChangesList instance.
&$s: HTML of the form "<li>...</li>" containing one RC entry.
&$rc: The RecentChange object.
&$classes: array of css classes for the <li> element

'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

'OtherBlockLogLink': Get links to the block log from extensions which blocks
users and/or IP addresses too.
$otherBlockLink: An array with links to other block logs
$ip: The requested IP address or username

'OutputPageBeforeHTML': A page has been processed by the parser and the
resulting HTML is about to be displayed.
$parserOutput: the parserOutput (object) that corresponds to the page
$text: the text that will be displayed, in HTML (string)

'OutputPageBodyAttributes': Called when OutputPage::headElement is creating the
body tag to allow for extensions to add attributes to the body of the page they
might need. Or to allow building extensions to add body classes that aren't of
high enough demand to be included in core.
$out: The OutputPage which called the hook, can be used to get the real title
$sk: The Skin that called OutputPage::headElement
&$bodyAttrs: An array of attributes for the body tag passed to Html::openElement

'OutputPageCheckLastModified': when checking if the page has been modified
since the last visit.
&$modifiedTimes: array of timestamps.
        The following keys are set: page, user, epoch

'OutputPageParserOutput': after adding a parserOutput to $wgOut
$out: OutputPage instance (object)
$parserOutput: parserOutput instance being added in $out

'OutputPageMakeCategoryLinks': Links are about to be generated for the page's
categories. Implementations should return false if they generate the category
links, so the default link generation is skipped.
$out: OutputPage instance (object)
$categories: associative array, keys are category names, values are category
  types ("normal" or "hidden")
$links: array, intended to hold the result. Must be an associative array with
  category types as keys and arrays of HTML links as values.

'OutputPageScriptsForBottomQueue': Allows adding modules to the bottom queue
that should be requested in a dedicated <script> request. In most cases you'll
want to use OutputPage::addModules instead (from another hook) which allows
ResourceLoader to better combine requests and allows the module load requests
to be cached better. Typically you'd only use this for user-specific modules.
$out: OutputPage instance
&$modules: Array of modules names to add to the bottom queue

'PageContentInsertComplete': After a new article is created.
$wikiPage: WikiPage created
$user: User creating the article
$content: New content as a Content object
$summary: Edit summary/comment
$isMinor: Whether or not the edit was marked as minor
$isWatch: (No longer used)
$section: (No longer used)
$flags: Flags passed to WikiPage::doEditContent()
$revision: New Revision of the article

'PageContentLanguage': Allows changing the language in which the content of a
page is written. Defaults to the wiki content language ($wgContLang).
$title: Title object
&$pageLang: the page content language (either an object or a language code)
$wgLang: the user language

'PageContentSave': Before an article is saved.
$wikiPage: the WikiPage (object) being saved
$user: the user (object) saving the article
$content: the new article content, as a Content object
$summary: the article summary (comment)
$isminor: minor flag
$iswatch: watch flag
$section: section #

'PageContentSaveComplete': After an article has been updated.
$wikiPage: WikiPage modified
$user: User performing the modification
$content: New content, as a Content object
$summary: Edit summary/comment
$isMinor: Whether or not the edit was marked as minor
$isWatch: (No longer used)
$section: (No longer used)
$flags: Flags passed to WikiPage::doEditContent()
$revision: New Revision of the article (can be null for edits that change nothing)
$status: Status object about to be returned by doEditContent()
$baseRevId: the rev ID (or false) this edit was based on

'PageHistoryBeforeList': When a history page list is about to be constructed.
$article: the article that the history is loading for
$context: RequestContext object

'PageHistoryLineEnding': Right before the end <li> is added to a history line.
$row: the revision row for this line
$s: the string representing this parsed line
$classes: array containing the <li> element classes

'PageHistoryPager::getQueryInfo': when a history pager query parameter set is
constructed.
$pager: the pager
$queryInfo: the query parameters

'PageRenderingHash': Alter the parser cache option hash key. A parser extension
which depends on user options should install this hook and append its values to
the key.
&$confstr: reference to a hash key string which can be modified
$user: User (object) requesting the page

'ParserAfterParse': Called from Parser::parse() just after the call to
Parser::internalParse() returns.
$parser: parser object
$text: text being parsed
$stripState: stripState used (object)

'ParserAfterStrip': Called at end of parsing time.
TODO: No more strip, deprecated ?
$parser: parser object
$text: text being parsed
$stripState: stripState used (object)

'ParserAfterTidy': Called after Parser::tidy() in Parser::parse()
$parser: Parser object being used
$text: text that will be returned

'ParserBeforeInternalParse': Called at the beginning of Parser::internalParse().
$parser: Parser object
$text: text to parse
$stripState: StripState instance being used

'ParserBeforeStrip': Called at start of parsing time.
TODO: No more strip, deprecated ?
$parser: parser object
$text: text being parsed
$stripState: stripState used (object)

'ParserBeforeTidy': Called before tidy and custom tags replacements.
$parser: Parser object being used
$text: actual text

'ParserClearState': Called at the end of Parser::clearState().
$parser: Parser object being cleared

'ParserCloned': Called when the parser is cloned.
$parser: Newly-cloned Parser object

'ParserFirstCallInit': Called when the parser initialises for the first time.
&$parser: Parser object being cleared

'ParserGetVariableValueSwitch': Called when the parser need the value of a
custom magic word
$parser: Parser object
$varCache: array to store the value in case of multiples calls of the
        same magic word
$index: index (string) of the magic
$ret: value of the magic word (the hook should set it)
$frame: PPFrame object to use for expanding any template variables

'ParserGetVariableValueTs': Use this to change the value of the time for the
{{LOCAL...}} magic word.
$parser: Parser object
$time: actual time (timestamp)

'ParserGetVariableValueVarCache': use this to change the value of the variable
cache or return false to not use it.
$parser: Parser object
$varCache: variable cache (array)

'ParserLimitReport': DEPRECATED, use ParserLimitReportPrepare and
ParserLimitReportFormat instead.
Called at the end of Parser:parse() when the parser will
include comments about size of the text parsed.
$parser: Parser object
&$limitReport: text that will be included (without comment tags)

'ParserLimitReportFormat': Called for each row in the parser limit report that
needs formatting. If nothing handles this hook, the default is to use "$key" to
get the label, and "$key-value" or "$key-value-text"/"$key-value-html" to
format the value.
$key: Key for the limit report item (string)
&$value: Value of the limit report item
&$report: String onto which to append the data
$isHTML: If true, $report is an HTML table with two columns; if false, it's
        text intended for display in a monospaced font.
$localize: If false, $report should be output in English.

'ParserLimitReportPrepare': Called at the end of Parser:parse() when the parser will
include comments about size of the text parsed. Hooks should use
$output->setLimitReportData() to populate data. Functions for this hook should
not use $wgLang; do that in ParserLimitReportFormat instead.
$parser: Parser object
$output: ParserOutput object

'ParserMakeImageParams': Called before the parser make an image link, use this
to modify the parameters of the image.
$title: title object representing the file
$file: file object that will be used to create the image
&$params: 2-D array of parameters
$parser: Parser object that called the hook

'ParserSectionCreate': Called each time the parser creates a document section
from wikitext. Use this to apply per-section modifications to HTML (like
wrapping the section in a DIV).  Caveat: DIVs are valid wikitext, and a DIV
can begin in one section and end in another. Make sure your code can handle
that case gracefully. See the EditSectionClearerLink extension for an example.
$parser: the calling Parser instance
$section: the section number, zero-based, but section 0 is usually empty
&$sectionContent: ref to the content of the section. modify this.
$showEditLinks: boolean describing whether this section has an edit link

'ParserTestParser': Called when creating a new instance of Parser in
tests/parser/parserTest.inc.
$parser: Parser object created

'ParserTestGlobals': Allows to define globals for parser tests.
&$globals: Array with all the globals which should be set for parser tests.
  The arrays keys serve as the globals names, its values are the globals values.

'ParserTestTables': Alter the list of tables to duplicate when parser tests are
run. Use when page save hooks require the presence of custom tables to ensure
that tests continue to run properly.
&$tables: array of table names

'PersonalUrls': Alter the user-specific navigation links (e.g. "my page,
my talk page, my contributions" etc).
&$personal_urls: Array of link specifiers (see SkinTemplate.php)
&$title: Title object representing the current page
$skin: SkinTemplate object providing context (e.g. to check if the user is logged in, etc.)

'PingLimiter': Allows extensions to override the results of User::pingLimiter().
&$user : User performing the action
$action : Action being performed
&$result : Whether or not the action should be prevented
Change $result and return false to give a definitive answer, otherwise
the built-in rate limiting checks are used, if enabled.
$incrBy: Amount to increment counter by

'PlaceNewSection': Override placement of new sections. Return false and put the
merged text into $text to override the default behavior.
$wikipage : WikiPage object
$oldtext : the text of the article before editing
$subject : subject of the new section
&$text : text of the new section

'PostLoginRedirect': Modify the post login redirect behavior.
Occurs after signing up or logging in, allows for interception of redirect.
&$returnTo: The page name to return to, as a string
&$returnToQuery: array of url parameters, mapping parameter names to values
&$type: type of login redirect as string;
  error: display a return to link ignoring $wgRedirectOnLogin
  signup: display a return to link using $wgRedirectOnLogin if needed
  success: display a return to link using $wgRedirectOnLogin if needed
  successredirect: send an HTTP redirect using $wgRedirectOnLogin if needed

'PreferencesGetLegend': Override the text used for the <legend> of a
preferences section.
$form: the PreferencesForm object. This is a ContextSource as well
$key: the section name
&$legend: the legend text. Defaults to wfMessage( "prefs-$key" )->text() but may be overridden

'PreferencesFormPreSave': Override preferences being saved
 $formData: array of user submitted data
 $form: PreferencesForm object, also a ContextSource
 $user: User object with preferences to be saved set
 &$result: boolean indicating success

'PrefixSearchBackend': Override the title prefix search used for OpenSearch and
AJAX search suggestions. Put results into &$results outparam and return false.
$ns : array of int namespace keys to search in
$search : search term (not guaranteed to be conveniently normalized)
$limit : maximum number of results to return
&$results : out param: array of page names (strings)

'PrefsEmailAudit': Called when user changes their email address.
$user: User (object) changing his email address
$oldaddr: old email address (string)
$newaddr: new email address (string)

'PrefsPasswordAudit': Called when user changes his password.
$user: User (object) changing his password
$newPass: new password
$error: error (string) 'badretype', 'wrongpassword', 'error' or 'success'

'ProtectionForm::buildForm': Called after all protection type fieldsets are made
in the form.
$article: the title being (un)protected
$output: a string of the form HTML so far

'ProtectionForm::save': Called when a protection form is submitted.
$article: the Page being (un)protected
&$errorMsg: an html message string of an error or an array of message name and
  its parameters
$reasonstr: a string describing the reason page protection level is altered

'ProtectionForm::showLogExtract': Called after the protection log extract is
shown.
$article: the page the form is shown for
$out: OutputPage object

'RawPageViewBeforeOutput': Right before the text is blown out in action=raw.
&$obj: RawAction object
&$text: The text that's going to be the output

'RecentChange_save': Called at the end of RecentChange::save().
$recentChange: RecentChange object

'RedirectSpecialArticleRedirectParams': Lets you alter the set of parameter
names such as "oldid" that are preserved when using redirecting special pages
such as Special:MyPage and Special:MyTalk.
&$redirectParams: An array of parameters preserved by redirecting special pages.

'RequestContextCreateSkin': Called when RequestContext::getSkin creates a skin
instance. Can be used by an extension override what skin is used in certain
contexts.
IContextSource $context: The RequestContext the skin is being created for.
&$skin: A variable reference you may set a Skin instance or string key on to
  override the skin that will be used for the context.

'ResetPasswordExpiration': Allow extensions to set a default password expiration
$user: The user having their password expiration reset
&$newExpire: The new expiration date

'ResetSessionID': Called from wfResetSessionID
$oldSessionID: old session id
$newSessionID: new session id

'ResourceLoaderGetConfigVars': Called at the end of
ResourceLoaderStartUpModule::getConfig(). Use this to export static
configuration variables to JavaScript. Things that depend on the current page
or request state must be added through MakeGlobalVariablesScript instead.
&$vars: array( variable name => value )

'ResourceLoaderRegisterModules': Right before modules information is required,
such as when responding to a resource
loader request or generating HTML output.
&$resourceLoader: ResourceLoader object

'ResourceLoaderTestModules': Let you add new JavaScript testing modules. This is
called after the addition of 'qunit' and MediaWiki testing resources.
&testModules: array of JavaScript testing modules. The 'qunit' framework,
  included in core, is fed using tests/qunit/QUnitTestResources.php.
&ResourceLoader object

To add a new qunit module named 'myext.tests':
testModules['qunit']['myext.tests'] = array(
        'script' => 'extension/myext/tests.js',
        'dependencies' => <any module dependency you might have>
);
For QUnit framework, the mediawiki.tests.qunit.testrunner dependency will be
added to any module.

'RevisionInsertComplete': Called after a revision is inserted into the database.
&$revision: the Revision
$data: the data stored in old_text.  The meaning depends on $flags: if external
  is set, it's the URL of the revision text in external storage; otherwise,
  it's the revision text itself.  In either case, if gzip is set, the revision
  text is gzipped.
$flags: a comma-delimited list of strings representing the options used.  May
  include: utf8 (this will always be set for new revisions); gzip; external.

'SearchGetNearMatchBefore': Perform exact-title-matches in "go" searches before
the normal operations.
$allSearchTerms : Array of the search terms in all content languages
&$titleResult : Outparam; the value to return. A Title object or null.

'SearchAfterNoDirectMatch': If there was no match for the exact result. This
runs before lettercase variants are attempted, whereas 'SearchGetNearMatch'
runs after.
$term : Search term string
&$title : Outparam; set to $title object and return false for a match

'SearchGetNearMatch': An extra chance for exact-title-matches in "go" searches
if nothing was found.
$term : Search term string
&$title : Outparam; set to $title object and return false for a match

'SearchGetNearMatchComplete': A chance to modify exact-title-matches in "go"
searches.
$term : Search term string
&$title : Current Title object that is being returned (null if none found).

'SearchResultInitFromTitle': Set the revision used when displaying a page in
search results.
$title : Current Title object being displayed in search results.
&$id: Revision ID (default is false, for latest)

'SearchableNamespaces': An option to modify which namespaces are searchable.
&$arr : Array of namespaces ($nsId => $name) which will be used.

'SelfLinkBegin': Called before a link to the current article is displayed to
allow the display of the link to be customized.
$nt: the Title object
&$html: html to display for the link
&$trail: optional text to display before $html
&$prefix: optional text to display after $html
&$ret: the value to return if your hook returns false

'SetupAfterCache': Called in Setup.php, after cache objects are set

'ShowMissingArticle': Called when generating the output for a non-existent page.
$article: The article object corresponding to the page

'ShowRawCssJs': Customise the output of raw CSS and JavaScript in page views.
DEPRECATED, use the ContentGetParserOutput hook instead!
$text: Text being shown
$title: Title of the custom script/stylesheet page
$output: Current OutputPage object

'ShowSearchHitTitle': Customise display of search hit title/link.
&$title: Title to link to
&$text: Text to use for the link
$result: The search result
$terms: The search terms entered
$page: The SpecialSearch object.

'ShowSearchHit': Customize display of search hit.
$searchPage: The SpecialSearch instance.
$result: The SearchResult to show
$terms: Search terms, for highlighting
&$link: HTML of link to the matching page. May be modified.
&$redirect: HTML of redirect info. May be modified.
&$section: HTML of matching section. May be modified.
&$extract: HTML of content extract. May be modified.
&$score: HTML of score. May be modified.
&$size: HTML of page size. May be modified.
&$date: HTML of of page modification date. May be modified.
&$related: HTML of additional info for the matching page. May be modified.
&$html: May be set to the full HTML that should be used to represent the search
  hit. Must include the <li> ... </li> tags. Will only be used if the hook
  function returned false.

'SiteNoticeBefore': Before the sitenotice/anonnotice is composed. Return true to
allow the normal method of notice selection/rendering to work, or change the
value of $siteNotice and return false to alter it.
&$siteNotice: HTML returned as the sitenotice
$skin: Skin object

'SiteNoticeAfter': After the sitenotice/anonnotice is composed.
&$siteNotice: HTML sitenotice. Alter the contents of $siteNotice to add to/alter
  the sitenotice/anonnotice.
$skin: Skin object

'SkinAfterBottomScripts': At the end of Skin::bottomScripts().
$skin: Skin object
&$text: bottomScripts Text. Append to $text to add additional text/scripts after
  the stock bottom scripts.

'SkinAfterContent': Allows extensions to add text after the page content and
article metadata. This hook should work in all skins. Set the &$data variable to
the text you're going to add.
&$data: (string) Text to be printed out directly (without parsing)
$skin: Skin object

'SkinBuildSidebar': At the end of Skin::buildSidebar().
$skin: Skin object
&$bar: Sidebar contents
Modify $bar to add or modify sidebar portlets.

'SidebarBeforeOutput': Allows to edit sidebar just before its output by skins.
$skin Skin object
&$bar: Sidebar content
Modify $bar to add or modify sidebar portlets.
Warning: This hook is run on each display. You should consider to use 'SkinBuildSidebar' that is aggressively cached.

'SkinCopyrightFooter': Allow for site and per-namespace customization of
copyright notice.
$title: displayed page title
$type: 'normal' or 'history' for old/diff views
&$msg: overridable message; usually 'copyright' or 'history_copyright'. This
  message must be in HTML format, not wikitext!
&$link: overridable HTML link to be passed into the message as $1
&$forContent: overridable flag if copyright footer is shown in content language.
  This parameter is deprecated.

'SkinGetPoweredBy': TODO
&$text: additional 'powered by' icons in HTML. Note: Modern skin does not use
the MediaWiki icon but plain text instead.
$skin: Skin object

'SkinSubPageSubtitle': At the beginning of Skin::subPageSubtitle().
&$subpages: Subpage links HTML
$skin: Skin object
$out: OutputPage object
If false is returned $subpages will be used instead of the HTML
subPageSubtitle() generates.
If true is returned, $subpages will be ignored and the rest of
subPageSubtitle() will run.

'SkinTemplateBuildNavUrlsNav_urlsAfterPermalink': After creating the "permanent
link" tab.
$sktemplate: SkinTemplate object
$nav_urls: array of tabs

'SkinTemplateGetLanguageLink': After building the data for a language link from
which the actual html is constructed.
&$languageLink: array containing data about the link. The following keys can be
  modified: href, text, title, class, lang, hreflang. Each of them is a string.
$languageLinkTitle: Title object belonging to the external language link
$title: Title object of the page the link belongs to

To alter the structured navigation links in SkinTemplates, there are three
hooks called in different spots:

'SkinTemplateNavigation': Called on content pages after the tabs have been
added, but before variants have been added.
'SkinTemplateNavigation::SpecialPage': Called on special pages after the special
tab is added but before variants have been added.
'SkinTemplateNavigation::Universal': Called on both content and special pages
after variants have been added.
&$sktemplate: SkinTemplate object
&$links: Structured navigation links. This is used to alter the navigation for
  skins which use buildNavigationUrls such as Vector.

'SkinTemplateOutputPageBeforeExec': Before SkinTemplate::outputPage() starts
page output.
&$sktemplate: SkinTemplate object
&$tpl: Template engine object

'SkinTemplatePreventOtherActiveTabs': Use this to prevent showing active tabs.
$sktemplate: SkinTemplate object
$res: set to true to prevent active tabs

'SkinTemplateTabAction': Override SkinTemplate::tabAction().
You can either create your own array, or alter the parameters for
the normal one.
&$sktemplate: The SkinTemplate instance.
$title: Title instance for the page.
$message: Visible label of tab.
$selected: Whether this is a selected tab.
$checkEdit: Whether or not the action=edit query should be added if appropriate.
&$classes: Array of CSS classes to apply.
&$query: Query string to add to link.
&$text: Link text.
&$result: Complete assoc. array if you want to return true.

'SkinTemplateToolboxEnd': Called by SkinTemplate skins after toolbox links have
been rendered (useful for adding more).
$sk: The QuickTemplate based skin template running the hook.
$dummy: Called when SkinTemplateToolboxEnd is used from a BaseTemplate skin,
  extensions that add support for BaseTemplateToolbox should watch for this
  dummy parameter with "$dummy=false" in their code and return without echoing
  any HTML to avoid creating duplicate toolbox items.

'SkinVectorStyleModules': Called when defining the list of module styles to be
loaded by the Vector skin.
$skin: SkinVector object
&$styles: Array of module names whose style will be loaded for the skin

'SoftwareInfo': Called by Special:Version for returning information about the
software.
$software: The array of software in format 'name' => 'version'. See
  SpecialVersion::softwareInformation().

'SpecialPageBeforeFormDisplay': Before executing the HTMLForm object.
$name: name of the special page
&$form: HTMLForm object

'SpecialBlockModifyFormFields': Add more fields to Special:Block
$sp: SpecialPage object, for context
&$fields: Current HTMLForm fields

'SpecialContributionsBeforeMainOutput': Before the form on Special:Contributions
$id: User id number, only provided for backwards-compatability
$user: User object representing user contributions are being fetched for
$sp: SpecialPage instance, providing context

'SpecialListusersDefaultQuery': Called right before the end of
UsersPager::getDefaultQuery().
$pager: The UsersPager instance
$query: The query array to be returned

'SpecialListusersFormatRow': Called right before the end of
UsersPager::formatRow().
$item: HTML to be returned. Will be wrapped in <li></li> after the hook finishes
$row: Database row object

'SpecialListusersHeader': Called before closing the <fieldset> in
UsersPager::getPageHeader().
$pager: The UsersPager instance
$out: The header HTML

'SpecialListusersHeaderForm': Called before adding the submit button in
UsersPager::getPageHeader().
$pager: The UsersPager instance
$out: The header HTML

'SpecialListusersQueryInfo': Called right before the end of.
UsersPager::getQueryInfo()
$pager: The UsersPager instance
$query: The query array to be returned

'SpecialMovepageAfterMove': Called after moving a page.
$movePage: MovePageForm object
$oldTitle: old title (object)
$newTitle: new title (object)

'SpecialNewpagesConditions': Called when building sql query for
Special:NewPages.
&$special: NewPagesPager object (subclass of ReverseChronologicalPager)
$opts: FormOptions object containing special page options
&$conds: array of WHERE conditionals for query
&tables: array of tables to be queried
&$fields: array of columns to select
&$join_conds: join conditions for the tables

'SpecialNewPagesFilters': Called after building form options at NewPages.
$special: the special page object
&$filters: associative array of filter definitions. The keys are the HTML
  name/URL parameters. Each key maps to an associative array with a 'msg'
  (message key) and a 'default' value.

'SpecialPage_initList': Called when setting up SpecialPageFactory::$list, use this
hook to remove a core special page.
$list: list (array) of core special pages

'SpecialPageAfterExecute': Called after SpecialPage::execute.
$special: the SpecialPage object
$subPage: the subpage string or null if no subpage was specified

'SpecialPageBeforeExecute': Called before SpecialPage::execute.
$special: the SpecialPage object
$subPage: the subpage string or null if no subpage was specified

'SpecialPasswordResetOnSubmit': When executing a form submission on
Special:PasswordReset.
$users: array of User objects.
$data: array of data submitted by the user
&$error: string, error code (message key) used to describe to error (out
  parameter). The hook needs to return false when setting this, otherwise it
  will have no effect.

'SpecialRandomGetRandomTitle': Called during the execution of Special:Random,
use this to change some selection criteria or substitute a different title.
&$randstr: The random number from wfRandom()
&$isRedir: Boolean, whether to select a redirect or non-redirect
&$namespaces: An array of namespace indexes to get the title from
&$extra: An array of extra SQL statements
&$title: If the hook returns false, a Title object to use instead of the
  result from the normal query

'SpecialRecentChangesFilters': Called after building form options at
RecentChanges. Deprecated, use ChangesListSpecialPageFilters instead.
$special: the special page object
&$filters: associative array of filter definitions. The keys are the HTML
  name/URL parameters. Each key maps to an associative array with a 'msg'
  (message key) and a 'default' value.

'SpecialRecentChangesPanel': Called when building form options in
SpecialRecentChanges.
&$extraOpts: array of added items, to which can be added
$opts: FormOptions for this request

'SpecialRecentChangesQuery': Called when building SQL query for
SpecialRecentChanges and SpecialRecentChangesLinked. Deprecated, use
ChangesListSpecialPageQuery instead.
&$conds: array of WHERE conditionals for query
&$tables: array of tables to be queried
&$join_conds: join conditions for the tables
$opts: FormOptions for this request
&$query_options: array of options for the database request
&$select: Array of columns to select

'SpecialResetTokensTokens': Called when building token list for
SpecialResetTokens.
&$tokens: array of token information arrays in the format of
  array( 'preference' => '<preference-name>', 'label-message' => '<message-key>' )

'SpecialSearchCreateLink': Called when making the message to create a page or
go to the existing page.
$t: title object searched for
&$params: an array of the default message name and page title (as parameter)

'SpecialSearchNogomatch': Called when user clicked the "Go" button but the
target doesn't exist.
&$title: title object generated from the text entered by the user

'SpecialSearchPowerBox': The equivalent of SpecialSearchProfileForm for
the advanced form, a.k.a. power search box.
&$showSections: an array to add values with more options to
$term: the search term (not a title object)
$opts: an array of hidden options (containing 'redirs' and 'profile')

'SpecialSearchProfiles': Allows modification of search profiles.
&$profiles: profiles, which can be modified.

'SpecialSearchProfileForm': Allows modification of search profile forms.
$search: special page object
&$form: String: form html
$profile: String: current search profile
$term: String: search term
$opts: Array: key => value of hidden options for inclusion in custom forms

'SpecialSearchSetupEngine': Allows passing custom data to search engine.
$search: SpecialSearch special page object
$profile: String: current search profile
$engine: the search engine

'SpecialSearchResultsPrepend': Called immediately before returning HTML
on the search results page.  Useful for including an external search
provider.  To disable the output of MediaWiki search output, return
false.
$specialSearch: SpecialSearch object ($this)
$output: $wgOut
$term: Search term specified by the user

'SpecialSearchResults': Called before search result display when there are
matches.
$term: string of search term
&$titleMatches: empty or SearchResultSet object
&$textMatches: empty or SearchResultSet object

'SpecialSearchNoResults': Called before search result display when there are no
matches.
$term: string of search term

'SpecialStatsAddExtra': Add extra statistic at the end of Special:Statistics.
&$extraStats: Array to save the new stats
  ( $extraStats['<name of statistic>'] => <value>; )

'SpecialUploadComplete': Called after successfully uploading a file from
Special:Upload.
$form: The SpecialUpload object

'SpecialVersionVersionUrl': Called when building the URL for Special:Version.
$wgVersion: Current $wgVersion for you to use
&$versionUrl: Raw url to link to (eg: release notes)

'SpecialWatchlistFilters': Called after building form options at Watchlist.
Deprecated, use ChangesListSpecialPageFilters instead.
$special: the special page object
&$filters: associative array of filter definitions. The keys are the HTML
  name/URL parameters. Each key maps to an associative array with a 'msg'
  (message key) and a 'default' value.

'SpecialWatchlistQuery': Called when building sql query for SpecialWatchlist.
Deprecated, use ChangesListSpecialPageQuery instead.
&$conds: array of WHERE conditionals for query
&$tables: array of tables to be queried
&$join_conds: join conditions for the tables
&$fields: array of query fields
$opts: A FormOptions object with watchlist options for the current request

'SpecialWatchlistGetNonRevisionTypes': Called when building sql query for
SpecialWatchlist. Allows extensions to register custom values they have
inserted to rc_type so they can be returned as part of the watchlist.
&$nonRevisionTypes: array of values in the rc_type field of recentchanges table

'TestCanonicalRedirect': Called when about to force a redirect to a canonical
URL for a title when we have no other parameters on the URL. Gives a chance for
extensions that alter page view behavior radically to abort that redirect or
handle it manually.
$request: WebRequest
$title: Title of the currently found title obj
$output: OutputPage object

'ThumbnailBeforeProduceHTML': Called before an image HTML is about to be
rendered (by ThumbnailImage:toHtml method).
$thumbnail: the ThumbnailImage object
&$attribs: image attribute array
&$linkAttribs: image link attribute array

'TitleArrayFromResult': Called when creating an TitleArray object from a
database result.
&$titleArray: set this to an object to override the default object returned
$res: database result used to create the object

'TitleQuickPermissions': Called from Title::checkQuickPermissions to add to
or override the quick permissions check.
$title: The Title object being accessed
$user: The User performing the action
$action: Action being performed
&$errors: Array of errors
$doExpensiveQueries: Whether to do expensive DB queries
$short: Whether to return immediately on first error

'TitleGetEditNotices': Allows extensions to add edit notices
$title: The Title object for the page the edit notices are for
$oldid: Revision ID that the edit notices are for (or 0 for latest)
&$notices: Array of notices. Keys are i18n message keys, values are parseAsBlock()ed messages.

'TitleGetRestrictionTypes': Allows extensions to modify the types of protection
that can be applied.
$title: The title in question.
&$types: The types of protection available.

'TitleIsCssOrJsPage': Called when determining if a page is a CSS or JS page.
$title: Title object that is being checked
$result: Boolean; whether MediaWiki currently thinks this is a CSS/JS page.
  Hooks may change this value to override the return value of
  Title::isCssOrJsPage().

'TitleIsAlwaysKnown': Called when determining if a page exists. Allows
overriding default behavior for determining if a page exists. If $isKnown is
kept as null, regular checks happen. If it's a boolean, this value is returned
by the isKnown method.
$title: Title object that is being checked
&$isKnown: Boolean|null; whether MediaWiki currently thinks this page is known

'TitleIsMovable': Called when determining if it is possible to move a page. Note
that this hook is not called for interwiki pages or pages in immovable
namespaces: for these, isMovable() always returns false.
$title: Title object that is being checked
$result: Boolean; whether MediaWiki currently thinks this page is movable.
  Hooks may change this value to override the return value of
  Title::isMovable().

'TitleIsWikitextPage': Called when determining if a page is a wikitext or should
be handled by separate handler (via ArticleViewCustom).
$title: Title object that is being checked
$result: Boolean; whether MediaWiki currently thinks this is a wikitext page.
  Hooks may change this value to override the return value of
  Title::isWikitextPage()

'TitleMove': Before moving an article (title).
$old: old title
$nt: new title
$user: user who does the move

'TitleMoveComplete': After moving an article (title).
$old: old title
$nt: new title
$user: user who did the move
$pageid: database ID of the page that's been moved
$redirid: database ID of the created redirect
$reason: reason for the move

'TitleReadWhitelist': Called at the end of read permissions checks, just before
adding the default error message if nothing allows the user to read the page. If
a handler wants a title to *not* be whitelisted, it should also return false.
$title: Title object being checked against
$user: Current user object
&$whitelisted: Boolean value of whether this title is whitelisted

'TitleSquidURLs': Called to determine which URLs to purge from HTTP caches.
$title: Title object to purge
&$urls: An array of URLs to purge from the caches, to be manipulated.

'UndeleteForm::showHistory': Called in UndeleteForm::showHistory, after a
PageArchive object has been created but before any further processing is done.
&$archive: PageArchive object
$title: Title object of the page that we're viewing

'UndeleteForm::showRevision': Called in UndeleteForm::showRevision, after a
PageArchive object has been created but before any further processing is done.
&$archive: PageArchive object
$title: Title object of the page that we're viewing

'UndeleteForm::undelete': Called un UndeleteForm::undelete, after checking that
the site is not in read-only mode, that the Title object is not null and after
a PageArchive object has been constructed but before performing any further
processing.
&$archive: PageArchive object
$title: Title object of the page that we're about to undelete

'UndeleteShowRevision': Called when showing a revision in Special:Undelete.
$title: title object related to the revision
$rev: revision (object) that will be viewed

'UnknownAction': An unknown "action" has occurred (useful for defining your own
actions).
$action: action name
$article: article "acted on"

'UnitTestsList': Called when building a list of files with PHPUnit tests.
&$files: list of files

'UnwatchArticle': Before a watch is removed from an article.
$user: user watching
$page: WikiPage object to be removed
&$status: Status object to be returned if the hook returns false

'UnwatchArticleComplete': After a watch is removed from an article.
$user: user that watched
$page: WikiPage object that was watched

'UpdateUserMailerFormattedPageStatus': Before notification email gets sent.
$formattedPageStatus: list of valid page states

'UploadForm:initial': Before the upload form is generated. You might set the
member-variables $uploadFormTextTop and $uploadFormTextAfterSummary to inject
text (HTML) either before or after the editform.
$form: UploadForm object

'UploadForm:BeforeProcessing': At the beginning of processUpload(). Lets you
poke at member variables like $mUploadDescription before the file is saved. Do
not use this hook to break upload processing. This will return the user to a
blank form with no error message; use UploadVerification and UploadVerifyFile
instead.
$form: UploadForm object

'UploadCreateFromRequest': When UploadBase::createFromRequest has been called.
$type: (string) the requested upload type
&$className: the class name of the Upload instance to be created

'UploadComplete': when Upload completes an upload.
&$upload: an UploadBase child instance

'UploadFormInitDescriptor': After the descriptor for the upload form as been
assembled.
$descriptor: (array) the HTMLForm descriptor

'UploadFormSourceDescriptors': after the standard source inputs have been
added to the descriptor
$descriptor: (array) the HTMLForm descriptor

'UploadVerification': Additional chances to reject an uploaded file. Consider
using UploadVerifyFile instead.
string $saveName: destination file name
string $tempName: filesystem path to the temporary file for checks
string &$error: output: message key for message to show if upload canceled by
  returning false. May also be an array, where the first element is the message
  key and the remaining elements are used as parameters to the message.

'UploadVerifyFile': extra file verification, based on mime type, etc. Preferred
in most cases over UploadVerification.
object $upload: an instance of UploadBase, with all info about the upload
string $mime: The uploaded file's mime type, as detected by MediaWiki. Handlers
  will typically only apply for specific mime types.
object &$error: output: true if the file is valid. Otherwise, an indexed array
  representing the problem with the file, where the first element is the message
  key and the remaining elements are used as parameters to the message.

'UploadComplete': Upon completion of a file upload.
$uploadBase: UploadBase (or subclass) object. File can be accessed by
  $uploadBase->getLocalFile().

'User::mailPasswordInternal': before creation and mailing of a user's new
temporary password
$user: the user who sent the message out
$ip: IP of the user who sent the message out
$u: the account whose new password will be set

'UserAddGroup': Called when adding a group; return false to override
stock group addition.
$user: the user object that is to have a group added
&$group: the group to add, can be modified

'UserArrayFromResult': Called when creating an UserArray object from a database
result.
&$userArray: set this to an object to override the default object returned
$res: database result used to create the object

'userCan': To interrupt/advise the "user can do X to Y article" check. If you
want to display an error message, try getUserPermissionsErrors.
$title: Title object being checked against
$user : Current user object
$action: Action being checked
$result: Pointer to result returned if hook returns false. If null is returned,
  userCan checks are continued by internal code.

'UserCanSendEmail': To override User::canSendEmail() permission check.
$user: User (object) whose permission is being checked
&$canSend: bool set on input, can override on output

'UserClearNewTalkNotification': Called when clearing the "You have new
messages!" message, return false to not delete it.
$user: User (object) that will clear the message
$oldid: ID of the talk page revision being viewed (0 means the most recent one)

'UserComparePasswords': Called when checking passwords, return false to
override the default password checks.
&$hash: String of the password hash (from the database)
&$password: String of the plaintext password the user entered
&$userId: Integer of the user's ID or Boolean false if the user ID was not
  supplied
&$result: If the hook returns false, this Boolean value will be checked to
  determine if the password was valid

'UserCreateForm': change to manipulate the login form
$template: SimpleTemplate instance for the form

'UserCryptPassword': Called when hashing a password, return false to implement
your own hashing method.
&$password: String of the plaintext password to encrypt
&$salt: String of the password salt or Boolean false if no salt is provided
&$wgPasswordSalt: Boolean of whether the salt is used in the default hashing
  method
&$hash: If the hook returns false, this String will be used as the hash

'UserEffectiveGroups': Called in User::getEffectiveGroups().
$user: User to get groups for
&$groups: Current effective groups

'UserGetAllRights': After calculating a list of all available rights.
&$rights: Array of rights, which may be added to.

'UserGetDefaultOptions': After fetching the core default, this hook is run right
before returning the options to the caller. Warning: This hook is called for
every call to User::getDefaultOptions(), which means it's potentially called
dozens or hundreds of times. You may want to cache the results of non-trivial
operations in your hook function for this reason.
&$defaultOptions: Array of preference keys and their default values.

'UserGetEmail': Called when getting an user email address.
$user: User object
&$email: email, change this to override local email

'UserGetEmailAuthenticationTimestamp': Called when getting the timestamp of
email authentication.
$user: User object
&$timestamp: timestamp, change this to override local email authentication
  timestamp

'UserGetImplicitGroups': Called in User::getImplicitGroups().
&$groups: List of implicit (automatically-assigned) groups

'UserGetLanguageObject': Called when getting user's interface language object.
$user: User object
&$code: Language code that will be used to create the object
$context: RequestContext object

'UserGetReservedNames': Allows to modify $wgReservedUsernames at run time.
&$reservedUsernames: $wgReservedUsernames

'UserGetRights': Called in User::getRights().
$user: User to get rights for
&$rights: Current rights

'UserIsBlockedFrom': Check if a user is blocked from a specific page (for
specific block exemptions).
$user: User in question
$title: Title of the page in question
&$blocked: Out-param, whether or not the user is blocked from that page.
&$allowUsertalk: If the user is blocked, whether or not the block allows users
  to edit their own user talk pages.

'UserIsBlockedGlobally': Check if user is blocked on all wikis.
&$user: User object
$ip: User's IP address
&$blocked: Whether the user is blocked, to be modified by the hook

'UserIsEveryoneAllowed': Check if all users are allowed some user right; return
false if a UserGetRights hook might remove the named right.
$right: The user right being checked

'UserLoadAfterLoadFromSession': Called to authenticate users on external or
environmental means; occurs after session is loaded.
$user: user object being loaded

'UserLoadDefaults': Called when loading a default user.
$user: user object
$name: user name

'UserLoadFromDatabase': Called when loading a user from the database.
$user: user object
&$s: database query object

'UserLoadFromSession': Called to authenticate users on external/environmental
means; occurs before session is loaded.
$user: user object being loaded
&$result: set this to a boolean value to abort the normal authentication
  process

'UserLoadOptions': When user options/preferences are being loaded from the
database.
$user: User object
&$options: Options, can be modified.

'UserLoginComplete': After a user has logged in.
$user: the user object that was created on login
$inject_html: Any HTML to inject after the "logged in" message.

'UserLoginForm': change to manipulate the login form
$template: SimpleTemplate instance for the form

'UserLogout': Before a user logs out.
$user: the user object that is about to be logged out

'UserLogoutComplete': After a user has logged out.
$user: the user object _after_ logout (won't have name, ID, etc.)
$inject_html: Any HTML to inject after the "logged out" message.
$oldName: name of the user before logout (string)

'UserRemoveGroup': Called when removing a group; return false to override stock
group removal.
$user: the user object that is to have a group removed
&$group: the group to be removed, can be modified

'UserRights': After a user's group memberships are changed.
$user  : User object that was changed
$add   : Array of strings corresponding to groups added
$remove: Array of strings corresponding to groups removed

'UserRequiresHTTPS': Called to determine whether a user needs
to be switched to HTTPS.
$user: User in question.
&$https: Boolean whether $user should be switched to HTTPS.

'UserResetAllOptions': Called in User::resetOptions() when user preferences
have been requested to be reset. This hook can be used to exclude certain
options from being reset even when the user has requested all prefs to be reset,
because certain options might be stored in the user_properties database table
despite not being visible and editable via Special:Preferences.
$user: the User (object) whose preferences are being reset
&$newOptions: array of new (site default) preferences
$options: array of the user's old preferences
$resetKinds: array containing the kinds of preferences to reset

'UserRetrieveNewTalks': Called when retrieving "You have new messages!"
message(s).
$user: user retrieving new talks messages
$talks: array of new talks page(s)

'UserSaveSettings': Called when saving user settings.
$user: User object

'UserSaveOptions': Called just before saving user preferences/options.
$user: User object
&$options: Options, modifiable

'UserSetCookies': Called when setting user cookies.
$user: User object
&$session: session array, will be added to $_SESSION
&$cookies: cookies array mapping cookie name to its value

'UserSetEmail': Called when changing user email address.
$user: User object
&$email: new email, change this to override new email address

'UserSetEmailAuthenticationTimestamp': Called when setting the timestamp of
email authentication.
$user: User object
&$timestamp: new timestamp, change this to override local email
authentication timestamp

'UserToolLinksEdit': Called when generating a list of user tool links, e.g.
"Foobar (Talk | Contribs | Block)".
$userId: User id of the current user
$userText: User name of the current user
&$items: Array of user tool links as HTML fragments

'ValidateExtendedMetadataCache': Called to validate the cached metadata in
FormatMetadata::getExtendedMeta (return false means cache will be
invalidated and GetExtendedMetadata hook called again).
$timestamp: The timestamp metadata was generated
$file: The file the metadata is for

'UserMailerChangeReturnPath': Called to generate a VERP return address
when UserMailer sends an email, with a bounce handling extension.
$to: Array of MailAddress objects for the recipients
&$returnPath: The return address string

'WantedPages::getQueryInfo': Called in WantedPagesPage::getQueryInfo(), can be
used to alter the SQL query which gets the list of wanted pages.
&$wantedPages: WantedPagesPage object
&$query: query array, see QueryPage::getQueryInfo() for format documentation

'WatchArticle': Before a watch is added to an article.
$user: user that will watch
$page: WikiPage object to be watched
&$status: Status object to be returned if the hook returns false

'WatchArticleComplete': After a watch is added to an article.
$user: user that watched
$page: WikiPage object watched

'WatchlistEditorBuildRemoveLine': when building remove lines in
Special:Watchlist/edit.
&$tools: array of extra links
$title: Title object
$redirect: whether the page is a redirect
$skin: Skin object

'WebRequestPathInfoRouter': While building the PathRouter to parse the
REQUEST_URI.
$router: The PathRouter instance

'WebResponseSetCookie': when setting a cookie in WebResponse::setcookie().
Return false to prevent setting of the cookie.
&$name: Cookie name passed to WebResponse::setcookie()
&$value: Cookie value passed to WebResponse::setcookie()
&$expire: Cookie expiration, as for PHP's setcookie()
$options: Options passed to WebResponse::setcookie()

'WhatLinksHereProps': Allows annotations to be added to WhatLinksHere
$row: The DB row of the entry.
$title: The Title of the page where the link comes FROM
$target: The Title of the page where the link goes TO
&$props: Array of HTML strings to display after the title.

'WikiExporter::dumpStableQuery': Get the SELECT query for "stable" revisions
dumps. One, and only one hook should set this, and return false.
&$tables: Database tables to use in the SELECT query
&$opts: Options to use for the query
&$join: Join conditions

'WikiPageDeletionUpdates': manipulate the list of DataUpdates to be applied when
a page is deleted. Called in WikiPage::getDeletionUpdates(). Note that updates
specific to a content model should be provided by the respective Content's
getDeletionUpdates() method.
$page: the WikiPage
$content: the Content to generate updates for
&$updates: the array of DataUpdate objects. Hook function may want to add to it.

'wfShellWikiCmd': Called when generating a shell-escaped command line string to
run a MediaWiki cli script.
&$script: MediaWiki cli script path
&$parameters: Array of arguments and options to the script
&$options: Associative array of options, may contain the 'php' and 'wrapper'
  keys

'wgQueryPages': Called when initialising list of QueryPage subclasses, use this
to add new query pages to be updated with maintenance/updateSpecialPages.php.
$qp: The list of QueryPages

'XmlDumpWriterOpenPage': Called at the end of XmlDumpWriter::openPage, to allow
extra metadata to be added.
$obj: The XmlDumpWriter object.
&$out: The output string.
$row: The database row for the page.
$title: The title of the page.

'XmlDumpWriterWriteRevision': Called at the end of a revision in an XML dump, to
add extra metadata.
$obj: The XmlDumpWriter object.
&$out: The text being output.
$row: The database row for the revision.
$text: The revision text.

'XMPGetInfo': Called when obtaining the list of XMP tags to extract. Can be used
to add additional tags to extract.
&$items: Array containing information on which items to extract. See XMPInfo for
  details on the format.

'XMPGetResults': Called just before returning the results array of parsing xmp
data. Can be used to post-process the results.
&$data: Array of metadata sections (such as $data['xmp-general']) each section
  is an array of metadata tags returned (each tag is either a value, or an array
  of values).

More hooks might be available but undocumented, you can execute
"php maintenance/findHooks.php" to find hidden ones.