Merge branch 'Wikidata' of ssh://gerrit.wikimedia.org:29418/mediawiki/core into Wikidata

[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

'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: name of error message to display on abort

'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)

'AfterFinalPageOutput': At the end of OutputPage::output() but before
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().

'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 sucessfully imported revisions
$pageInfo: associative array of page information

'AjaxAddScript': Called in output page just before the initialisation
of the javascript ajax engine. The hook is only called when ajax
is enabled ( $wgUseAjax = true; ).

'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

'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

'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

'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 mofify the properties
in a module's result.
&$module: ApiBase Module object
&$properties: Array of properties

'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

'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)

'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.

'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
$output: the OutputPage object ($wgOut)
&$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
 $output: the OutputPage object ($wgOut)

'ArticleDelete': before an article is deleted
$article: 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)

'ArticleDeleteComplete': after an article is deleted
$article: 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

'ArticleEditUpdateNewTalk': before updating user_newtalk when a user talk page
was changed
$article: WikiPage (object) of the user talk page

'ArticleEditUpdates': when edit updates (mainly link tracking) are made when an
article has been changed
$article: 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
$article: 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

'ArticleInsertComplete': After a new article is created. DEPRECATED, use ArticleContentInsertComplete
$article: 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 Article::doEdit()
$revision: New Revision of the article

'ArticleContentInsertComplete': After a new article is created
$article: 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 Article::doEdit()
$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
$article: WikiPage (object) whose data were loaded
$row: row (object) returned from the database server

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

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

'ArticleProtect': before an article is protected
$article: 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
$article: 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"
$article: WikiPage (object) to purge

'ArticleRevisionVisibilitySet': called when changing visibility of one or more
revision 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
$article: 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 ArticleContentSave instead
$article: 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 #

'ArticleContentSave': before an article is saved.
$article: 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 #

'ArticleSaveComplete': After an article has been updated. DEPRECATED, use ArticleContentSaveComplete instead.
$article: 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 Article::doEdit()
$revision: New Revision of the article
$status: Status object about to be returned by doEdit()
$baseRevId: the rev ID (or false) this edit was based on

'ArticleContentSaveComplete': After an article has been updated
$article: 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 Article::doEdit()
$revision: New Revision of the article
$status: Status object about to be returned by doEdit()
$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.

'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

'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
follwed an redirect
$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 preferrable 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 preferrable 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 ($wgAuth)
Gives a chance for an extension to set it programattically to a variable class.
&$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 spefific 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
$name: Image name being checked
&$bad: Whether or not the image is "bad"

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.

'BeforeDisplayNoArticleText': before displaying 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

'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

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)

'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

'CanonicalNamespaces': For extensions adding their own namespaces or altering the defaults
&$namespaces: Array of namespace numbers with corresponding canonical names

'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.

'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 determiend
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
cointent 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.

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

'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

'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

'Debug': called when outputting a debug log line via wfDebug() or wfDebugLog()
$text: plaintext string to be output
$group: null or a string naming a logging group (as defined in $wgDebugLogGroups)

'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

'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
  $wgTitle, 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"
$tooltip: The default tooltip.  Escape with htmlspecialchars() before using.
  By default, this is wrapped in the 'editsectionhint' message.
&$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 wfMsg* functions

'EditFilter': Perform checks on an edit
$editor: 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
$editor: EditPage instance (object)
$content: content of the edit box, as a Content object
&$error: error message to return
$summary: Edit summary for page

'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 Article::doEdit() 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.

'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': Allow modifying the wikitext that will be used in
"Show changes". DEPRECATED. Use EditPageGetDiffContent instead.
Note that it is preferrable 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 preferrable 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': Allow modifying the wikitext that will be previewed.
DEPRECATED. Use EditPageGetPreviewContent instead.
Note that it is preferrable 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 preferrable 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'

'EditSectionLink': Do not use, use DoEditSectionLink instead.
$skin: Skin rendering the UI
$title: Title being linked to
$section: Section to link to
$link: Default link
&$result: Result (alter this to override the generated links)
$lang: The language code to use for the link in the wfMsg* functions

'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
$thumbname: the base name of the thumbnail file
&$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.

'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.

'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()

'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)

'GetMetadataVersion': modify the image metadata version currently in use. This is
        used when requesting image metadata from a ForiegnApiRepo. 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

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

'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': Absolutely the same, but is called only
        if expensive checks are enabled.

'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.


'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::makeImageLink2
&$handlerParams: Various parameters with special meanings; see documentation in
        includes/Linker.php for Linker::makeImageLink2
&$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 contructed
$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

'InitializeArticleMaybeRedirect': MediaWiki check to see if title is a redirect
$title: Title object ($wgTitle)
$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.

'InternalParseBeforeLinks': during Parser's internalParse method before links
but after noinclude/includeonly/onlyinclude and other processing.
&$parser: Parser object
&$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

'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()

'isValidEmailAddr': Override the result of User::isValidEmailAddr(), for ins-
tance 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: laguage 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: laguage code (string)

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

'LinkBegin': Used when generating internal and interwiki links in
Linker::link(), before processing starts.  Return false to skip default proces-
sing 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 "de-
        fault"
&$customAttribs: the HTML attributes that the <a> tag should have, in associa-
        tive array form, with keys and values unescaped.  Should be merged with de-
        fault values, with a value of false meaning to suppress the attribute.
&$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 re-
turn 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.
&$attribs: the final HTML attributes of the <a> tag, after processing, in asso-
        ciative array form.
&$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

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

'LinksUpdateComplete': At the end of LinksUpdate::doUpdate() when updating has
completed
&$linksUpdate: the LinksUpdate object

'LinksUpdateConstructed': At the end of LinksUpdate() is contruction.
&$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

'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 wfMsgExt and option 'parse'
 - 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)

'LoggableUserIPData': called when IP data for a user action can be logged by extensions like CheckUser.
This is intended for when users do things that do not already create edits or log entries.
$context: The context the of the action, which includes the user and request
$data: Associative array of data for handlers to record. It must include values for:
 - 'namespace' Integer namespace for target title (NS_SPECIAL is allowed)
 - 'title'     Database key string for target title (empty string if not applicable)
 - 'pageid'    Integer page ID for target title (zero if not applicable)
 - 'action'    Wikitext string in the same format as an edit summary
 - 'comment'   Wikitext string in the same format as an edit summary
 - 'timestamp' Timestamp when the action occured

'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)

'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)

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

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

'MakeGlobalVariablesScript': called right before Skin::makeVariablesScript
is executed. 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: $wgArticle
$title: $wgTitle
$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

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

'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': Called by Monobook skin after toolbox links have
been rendered (useful for adding more)
Note: this is only run for the Monobook skin. This hook is deprecated and
may be removed in the future. 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
$article: 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.
&$changeslist: The OldChangesList instance.
&$s: HTML of the form "<li>...</li>" containing one RC entry.
&$rc: The RecentChange object.

'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.

'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

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

'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.
$hash: reference to a hash key string which can be modified

'ParserAfterStrip': Same as ParserBeforeStrip

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

'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: varaiable cache (array)

'ParserLimitReport': 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)

'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
maintenance/parserTests.inc
$parser: Parser object created

'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

'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.

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

'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 wfMsg( "prefs-$key" ) but may be overridden

'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 his 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 passoword
$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 title being (un)protected
$errorMsg: an html message string of an error or an array of message name and its parameters

'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
&$obj: RawPage object
&$text: The text that's going to be the output

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

'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.

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

'ResourceLoaderGetStartupModules': Run once the startup module is being generated. This allows you
to add modules to the startup module. This hook should be used sparingly since any module added here
will be loaded on all pages. This hook is useful if you want to make code available to module loader
scripts.

'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 DB
&$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.

'SearchUpdate': Prior to search update completion
$id : Page id
$namespace : Page namespace
$title : Page title
$text : Current text being indexed

'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.

'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).

'SearchEngineReplacePrefixesComplete': Run after SearchEngine::replacePrefixes().
$searchEngine : The SearchEngine object. Users of this hooks will be interested
in the $searchEngine->namespaces array.
$query : Original query.
&$parsed : Resultant query with the prefixes stripped.

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

'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 ContentHandler facility to handle CSS and JavaScript!
$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.

'SiteNoticeBefore': Before the sitenotice/anonnotice is composed
&$siteNotice: HTML returned as the sitenotice
$skin: Skin object
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.

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

'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.
&$data: (string) Text to be printed out directly (without parsing)
$skin: Skin object
This hook should work in all skins. Just set the &$data variable to the text
you're going to add.

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

'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.

'SkinGetPoweredBy'
&$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

Alter the structured navigation links in SkinTemplates, there are three of these hooks called in different spots.
'SkinTemplateNavigation': Called on content pages after the tabs have been added but before 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.

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

'SpecialContributionsBeforeMainOutput': Before the form on Special:Contributions
$id: User identifier

'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 SpecialPage::$mList, use this
hook to remove a core special page
$list: list (array) of core special pages

'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 name) used to describe to error (out paramater).
        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
$special: the special page object
&$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
&$conds: array of WHERE conditionals for query
&$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

'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)

'SpecialSearchGo': called when user clicked the "Go"
&$title: title object generated from the text entered by the user
&$term: the search term entered by the user

'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: special page object
$profile: String: current search profile
$engine: the search engine

'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

'SpecialVersionExtensionTypes': called when generating the extensions credits,
use this to change the tables headers
$extTypes: associative array of extensions types

'SpecialWatchlistFilters': called after building form options at Watchlist
$special: the special page object
&$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
&$conds: array of WHERE conditionals for query
&$tables: array of tables to be queried
&$join_conds: join conditions for the tables
&$fields: array of query fields

'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

'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

'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 behaviour 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
$result: 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 seperate 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()

'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

'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

'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 occured (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

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

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

'UploadForm:BeforeProcessing': at the beginning of processUpload()
$form: UploadForm object
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

'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'll clear the message

'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 ran
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 authentification
$user: User object
&$timestamp: timestamp, change this to override local email authentification
        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: Langauge code that will be used to create the 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

'UserLoadAfterLoadFromSession': called to authenticate users on
external/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 authentification
        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

'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 authentification
$user: User object
&$timestamp: new timestamp, change this to override local email
authentification timestamp

'UserToolLinksEdit': Called when generating a list of user tool links, eg "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

'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

'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

'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 ContentHandler's getDeletionUpdates() method.
$page: the WikiPage
&$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 $wgQueryPages, use this to add new
query pages to be updated with maintenance/updateSpecialPages.php
$query: $wgQueryPages itself

'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
./maintenance/findhooks.php to find hidden one.