Release notes/1.27

= MediaWiki release notes =

MediaWiki 1.27.2
This is a security and maintenance release of the MediaWiki 1.27 branch.

ApiCreateAccount was removed in 1.27.0. It was incorrectly still marked as deprecated (rather than already removed) in the RELEASE-NOTES at the point 1.27.0 was released.

Changes since 1.27.1

 * (T68404) CSS3 attr function with url type argument is no longer allowed in inline styles.
 * $wgRunJobsAsync is now false by default (T142751). This change only affects wikis with $wgJobRunRate > 0.
 * (T152717) Better escaping for PHP mail command
 * Submitting the lgtoken and lgpassword parameters in the query string to action=login is now deprecated and outputs a warning. They should be submitted in the POST body instead.
 * Submitting sensitive authentication request parameters to action=clientlogin, action=createaccount, action=linkaccount, and action=changeauthenticationdata in the query string is now deprecated and outputs a warning. They should be submitted in the POST body instead.
 * (T158766) Avoid SQL error on MSSQL when using selectRowCount
 * (T145635) Fix too long index error when installing with MSSQL.
 * (T156184) $wgRawHtml will no longer apply to internationalization messages.
 * (T160519) CACHE_ANYTHING will not be CACHE_ACCEL if no accelerator is installed.
 * (T109140) (T122209) SECURITY: Special:UserLogin and Special:Search allow redirect to interwiki links.
 * (T144845) SECURITY: XSS in SearchHighlighter::highlightText when $wgAdvancedSearchHighlighting is true.
 * (T125177) SECURITY: API parameters may now be marked as "sensitive" to keep their values out of the logs.
 * (T150044) SECURITY: "Mark all pages visited" on the watchlist now requires a CSRF token.
 * (T156184) SECURITY: Escape content model/format url parameter in message.
 * (T151735) SECURITY: SVG filter evasion using default attribute values in DTD declaration.
 * (T161453) SECURITY: LocalisationCache will no longer use the temporary directory in it's fallback chain when trying to work out where to write the cache.
 * (T48143) SECURITY: Spam blacklist ineffective on encoded URLs inside file inclusion syntax's link parameter.
 * (T108138) SECURITY: Sysops can undelete pages, although the page is protected against it.

MediaWiki 1.27.1
This is a security and maintenance release of the MediaWiki 1.27 branch.

Changes since 1.27.0

 * BREAKING CHANGE: $wgHTTPProxy is now *required* for all external requests made by MediaWiki via a proxy. Relying on the http_proxy environment variable is no longer supported.
 * (T139565) SECURITY: API: Generate head items in the context of the given title
 * (T137264) SECURITY: XSS in unclosed internal links
 * (T133147) SECURITY: Escape '<' and ']]>' in inline blocks
 * (T133147) SECURITY: Require login to preview user CSS pages
 * (T132926) SECURITY: Do not allow undeleting a revision deleted file if it is the top file
 * (T129738) SECURITY: Make $wgBlockDisablesLogin also restrict logged in permissions
 * (T129738) SECURITY: Make blocks log users out if $wgBlockDisablesLogin is true
 * (T115333) SECURITY: Check read permission when loading page content in ApiParse
 * (T57548) Remove support for $wgWellFormedXml = false, all output is now well formed
 * (T139670) Move 'UserGetRights' call before application of Session::getAllowedUserRights

PHP version requirement
As of 1.27, MediaWiki now requires PHP 5.5.9 or higher (see Compatibility section). Additionally, the following PHP extensions are required:

The following PHP extensions are strongly recommended:
 * ctype
 * iconv
 * json
 * mbstring (new requirement in 1.27)
 * xml
 * openssl

Configuration changes

 * and were removed, now always enabled. If you use RDFa on your wiki, you now have to explicitly set  to 'HTML+RDFa 1.0' or 'XHTML+RDFa 1.0'.
 * was removed.
 * Deprecated and, because there was little value in making the behavior configurable. The default values (`false` for the former, 1000 for the latter) are now hard-coded.
 * was removed (deprecated in 1.24).
 * was removed (deprecated in 1.20).
 * has been removed, as it provides functionality only used by custom Wikimedia patches against Squid 2.x that probably noone uses in production anymore. There is now that provides similar functionality but instead of the MediaWiki-specific X-Vary-Options header, uses the draft Key header standard.
 * (and support for '.php5' entry points) was removed. See the deprecation notice in the release notes for version 1.25 for advice on how to preserve support for '.php5' entry points via URL rewriting.
 * Password handling via the User object has been deprecated and partially removed, pending the future introduction of AuthManager. In particular:
 * expirePassword, getPasswordExpireDate, resetPasswordExpiration, and getPasswordExpired have been removed. They were unused outside of core.
 * The mPassword, mNewpassword, mNewpassTime, and mPasswordExpires fields are now private and will be removed in the future.
 * The getPassword and getTemporaryPassword methods now throw BadMethodCallException and will be removed in the future.
 * The ability to pass 'password' and 'newpassword' to createNew has been removed. The only users of it seem to have been using it to set invalid passwords, and so shouldn't be greatly affected.
 * setPassword, setInternalPassword, and setNewpassword have been deprecated, pending the introduction of AuthManager.
 * User::randomPassword is deprecated in favor of a new method PasswordFactory::generateRandomPasswordString
 * User::getPasswordFactory is deprecated, callers should just create a PasswordFactory themselves.
 * A new constructor, User::newSystemUser, has been added to simplify the creation of passwordless "system" users for logged actions.
 * was removed.
 * was removed. This is now enabled by default.
 * now hotlinks Commons images by default instead of downloading originals and thumbnailing them locally. This allows wikis to save on CPU and bandwidth while reducing time to first byte for pages, even without a thumbnail handler. See documentation for tweaks.
 * WebP is enabled by default as an uploadable filetype.
 * must now be either a full url, or start with a "/".
 * was removed; use ['ratelimit'] instead.
 * Deprecated API formats dbg, txt, and yaml have been removed.
 * CLDRPluralRule* classes have been replaced with wikimedia/cldr-plural-rule-parser.
 * Removed, , , , , , , and (deprecated since 1.20).
 * For proper operation of LocalIdLookup with shared user tables, ensure that and  are properly set even on the "central" wiki that all others are sharing from and that  is set to the full list of sharing wikis on all those wikis.
 * Massive overhaul to session handling:
 * is no longer supported and must be true, due to MediaWiki\Session\SessionManager. is similarly no longer used.
 * ObjectCacheSessionHandler is removed, replaced with MediaWiki\Session\PhpSessionHandler.
 * PHP session handling in general ($_SESSION, session_id, and so on) is deprecated. Use MediaWiki\Session\SessionManager instead. A new config variable,, is available to cause use of $_SESSION to issue a deprecation warning or to cause most PHP session handling to throw exceptions.
 * Deprecated UserSetCookies hook. Session-handling extensions should generally be creating a custom subclass of CookieSessionProvider. Other extensions messing with cookies can no longer count on user data being saved in cookies versus other methods.
 * Deprecated UserLoadFromSession hook, extensions should create a MediaWiki\Session\SessionProvider.
 * The User cannot be loaded from session until after Setup.php completes. Attempts to do so will be ignored and the User will remain unloaded.
 * CSRF tokens may be fetched from the MediaWiki\Session\Session, which uses the MediaWiki\Session\Token class.
 * MediaWiki will now auto-create users as necessary, removing the need for extensions to do so. An 'autocreateaccount' right is added to allow auto-creation when 'createaccount' is not granted to all users.
 * Deprecated AuthPluginAutoCreate hook in favor of LocalUserCreated.
 * Most cookie-handling methods in User are deprecated.
 * and $CopyUploadAsyncTimeout were removed. This was an experimental feature that has never worked.
 * Login and createaccount tokens now vary by timestamp.
 * LoginForm::getLoginToken and LoginForm::getCreateaccountToken return a MediaWiki\Session\Token, and tokens must be checked using that class's methods.
 * was removed and the job queue is always used.
 * The functionality of the ApiSandbox extension has been merged into core. The extension should no longer be used.
 * was removed (deprecated in 1.26). Extensions, skins, gadgets and scripts that use the mediawiki.util module must express a dependency on it.
 * , deprecated in MediaWiki 1.26, now defaults false. Extensions, skins, gadgets and scripts that need the mediawiki.legacy.wikibits module should express a dependency on it.
 * Removed configuration option (deprecated since 1.18). Use ['copyright']['copyright'] instead.
 * If the openssl and mcrypt PHP extensions are both unavailable, secure session storage (used for login) will raise an exception. This exception may be bypassed by setting = true.
 * Massive overhaul to authentication:
 * AuthPlugin and AuthPluginUser are deprecated.
 * LoginForm and associated templates are deprecated. Extensions which called static LoginForm methods should be converted into authentication providers.
 * The following hooks are deprecated:
 * AbortAutoAccount (create a MediaWiki\Auth\PreAuthenticationProvider instead)
 * AbortLogin (create a MediaWiki\Auth\PreAuthenticationProvider instead)
 * AbortNewAccount (create a MediaWiki\Auth\PreAuthenticationProvider instead)
 * AddNewAccount (use LocalUserCreated instead)
 * AuthPluginSetup (create a MediaWiki\Auth\PrimaryAuthenticationProvider instead)
 * ChangePasswordForm (use AuthChangeFormFields instead, or security levels)
 * LoginUserMigrated (create a MediaWiki\Auth\PreAuthenticationProvider instead)
 * UserCreateForm (create a MediaWiki\Auth\AuthenticationProvider of some type instead)
 * UserLoginForm (create a MediaWiki\Auth\AuthenticationProvider of some type instead)
 * The following hooks are removed:
 * AbortChangePassword
 * LoginPasswordResetMessage
 * PrefsPasswordAudit
 * The UserLoginComplete hook will no longer be called for all logins, only for those via the web UI. Use UserLoggedIn if you need to do something on all logins.
 * is removed.
 * has been removed.

New features

 * was also added. This decides how long a user sticks to the primary DC (via cookies) after they make changes to the site.
 * Added a new hook, 'UserMailerTransformContent', to transform the contents of an email. This is similar to the EmailUser hook but applies to all mail sent via UserMailer.
 * Added a new hook, 'UserMailerTransformMessage', to transform the contents of an emai after MIME encoding.
 * Added a new hook, 'UserMailerSplitTo', to control which users have to be emailed separately (ie. there is a single address in the To: field) so user-specific changes to the email can be applied safely.
 * was added, which limits the CDN cache TTL when any load balancer uses a DB that is lagged beyond the 'max lag' setting in the relevant section of.
 * User::newSystemUser may be used to simplify the creation of passwordless "system" users for logged actions from scripts and extensions.
 * Extensions can now return detailed error information via the API when preventing user actions using 'getUserPermissionsErrors' and similar hooks by using ApiMessage instances instead of strings for the $result value.
 * was added to limit bot changes when databases lag becomes too high.
 * Skins and extensions can now use FlexBox mixins (.flex-display(@display: flex) and .flex(@grow: 1, @shrink: 1, @width: auto, @order: 1)) in Less to create cross-browser-compatible FlexBox rules. Users will still need to add fallback float rules or the like for compatibility with IE9- separately.
 * Added MWTimestamp::getTimezoneString which returns the localized timezone string, if available. To localize this string, see the comments of in includes/DefaultSettings.php.
 * Added CentralIdLookup, a service that allows extensions needing a concept of "central" users to get that without having to know about specific central authentication extensions.
 * added to limit huge user-generated transactions. Regular web request transactions that takes longer than this are aborted.
 * Added a new hook, 'TitleMoveCompleting', which runs before a page move is committed.
 * was added to provide secondary delayed purges of URLs from CDN to mitigate DB replication lag and WAN cache purge lag.
 * Installer will default to setting CACHE_ACCEL as the main cache type if it is available.
 * It is now possible to patrol file uploads (both for new files and new versions of existing files). Special:NewFiles has gained an option to filter by patrol status. This functionality can be disabled using.
 * MediaWiki\Session infrastructure allows for easier use of session mechanisms other than the usual cookies.
 * SessionMetadata and SessionCheckInfo hooks allow for setting and checking custom session metadata.
 * Added MWGrants and associated configuration settings and  to hold configuration for authentication features such as OAuth that want to allow restricting the user rights a user may make use of.
 * If you're already using the OAuth extension, these new variables are identical to (and will replace) and.
 * Added MWRestrictions as a class to check restrictions on a WebRequest, e.g. to assert that the request comes from a particular IP range.
 * Added bot passwords, a rights-restricted login mechanism for API-using bots.
 * Whitelisted the following HTML attributes for all elements in wikitext: aria-describedby, aria-flowto, aria-label, aria-labelledby, aria-owns.
 * Removed "presentation" restriction on the HTML role attribute in wikitext. All values are now allowed for the role attribute.
 * now also supports callbacks to create an instance of the appropriate ContentHandler subclass.
 * Added, which if non-null prevents the user_token database field from being exposed in cookies. Setting this would be a good idea, but will log out all current sessions.
 * was added, for managing PubSub event relay configuration, specifically for reliable CDN url purges.
 * Requests have unique IDs, equal to the UNIQUE_ID environment variable (when MediaWiki is behind Apache+mod_unique_id or something similar) or a randomly- generated 24-character string. This request ID is used to annotate log records and error messages. It is available client-side via mw.config.get( 'wgRequestId' ). The request ID supplants exception IDs. Accordingly, MWExceptionHandler::getLogId is deprecated.
 * Add a preference for watching uploads by default, also applies to API-based upload tools.
 * was added to override chroma subsampling for JPEG image thumbnails created via ImageMagick. Defaults to 'yuv420', providing bandwidth savings versus the previous behavior on many files.
 * MediaWiki\Auth infrastructure (called "AuthManager") allows for more flexible configuration of multiple authentication pieces that was possible with AuthPlugin. For example, it's now easy to plug in second-factor authentication, or add additional checks to the login process, or to support multiple login methods at once, or to support non-password-based login methods.
 * Providers are configured via the global setting.
 * New hook, AuthChangeFormFields, to adjust the form fields on AuthManager-related special pages.
 * New hook, AuthManagerLoginAuthenticateAudit, for additional logging of AuthManager-related authentication requests.
 * New hook, ChangeAuthenticationDataAudit, for additional logging of AuthManager-related authentication data changes.
 * New hook, SecuritySensitiveOperationStatus, to work with the new mechanism for requiring a recent login before taking security-sensitive operations like changing a password.
 * Two new globals, and  can be used to prevent the web UI and the API changing certain authentication data.
 * The file upload dialog (available if you install WikiEditor or VisualEditor) can now be configured using.

Upgraded external libraries

 * Updated oojs/oojs-ui from v0.12.12 to v0.13.3.
 * Updated composer/semver from v1.0.0 to v1.2.0.
 * Updated liuggio/statsd-php-client to 1.0.18.
 * Updated QUnit from v1.18.0 to v1.22.0.

New external libraries

 * Added wikimedia/base-convert v1.0.1.
 * Added wikimedia/cldr-plural-rule-parser v1.0.0.
 * Added wikimedia/relpath v1.0.3.
 * Added wikimedia/running-stat v1.1.0.
 * Added wikimedia/php-session-serializer v1.0.3.

Bug fixes

 * Special:Upload will now display correct maximum allowed file size when running under HHVM.
 * The APIEditBeforeSave hook will once again give only the content of the section being edited, rather than the whole revision. This reverts the change made in MediaWiki 1.22.

Action API changes

 * Added list=allrevisions.
 * generator=recentchanges now has the option to generate revids.
 * ApiPageSet::setRedirectMergePolicy was added. This allows generator modules to define how generator data for a redirect source gets merged into the redirect destination.
 * prop=imageinfo&iiprop=uploadwarning will no longer include the possibility of "was-deleted" warning.
 * Added difftotextpst to query=revisions which preforms a pre-save transform on the text before diffing it.
 * Deprecated formats dbg, txt, and yaml have been removed.
 * The protect log event details now use new-style formatting.
 * The following response properties from action=login are deprecated, and may be removed in the future: lgtoken, cookieprefix, sessionid. Clients should handle cookies to properly manage session state.
 * action=login transparently allows login using bot passwords. Clients should merely need to change the username and password used after setting up a bot password.
 * action=upload no longer understands statuskey, asyncdownload or leavemessage.
 * action=login is deprecated for uses other than bot passwords.
 * list=users can now indicate if a missing username is creatable.
 * action=createaccount is changed in a non-backwards-compatible manner.
 * Added action=query&meta=authmanagerinfo.
 * Added action=clientlogin to be used to log into the main account instead of action=login.
 * Added action=linkaccount.
 * Added action=unlinkaccount.
 * Added action=changeauthenticationdata.
 * Added action=removeauthenticationdata.
 * Added action=resetpassword.

Action API internal changes

 * ApiQueryORM removed.
 * The following classes have been removed:
 * ApiFormatDbg
 * ApiFormatTxt
 * ApiFormatYaml
 * ApiBase::addTokenProperties was removed (deprecated since 1.24).
 * ApiBase::getFinalPossibleErrors was removed (deprecated since 1.24).
 * ApiBase::getFinalResultProperties was removed (deprecated since 1.24).
 * ApiBase::getRequireAtLeastOneParameterErrorMessages was removed (deprecated since 1.24).
 * ApiBase::getPossibleErrors was removed (deprecated since 1.24).
 * ApiBase::getRequireMaxOneParameterErrorMessages was removed (deprecated since 1.24).
 * ApiBase::getRequireOnlyOneParameterErrorMessages was removed (deprecated since 1.24).
 * ApiBase::getResultProperties was removed (deprecated since 1.24).
 * ApiBase::getTitleOrPageIdErrorMessage was removed (deprecated since 1.24).
 * ApiBase::parseErrors was removed (deprecated since 1.24).
 * ApiQueryBase::titleToKey, ApiQueryBase::keyToTitle and ApiQueryBase::keyPartToTitle all removed (deprecated since 1.24).
 * ApiQueryBase::checkRowCount was removed (deprecated since 1.24).
 * ApiQueryBase::getDirectionDescription was removed (deprecated since 1.25).
 * ApiQuery::getGenerators was removed (deprecated since 1.21).
 * ApiQuery::getModules was removed (deprecated since 1.21).
 * ApiQuery::getModuleType was removed (deprecated since 1.21).
 * ApiQuery::setGeneratorContinue was removed (deprecated since 1.24).
 * ApiMain::getModules was removed (deprecated since 1.21).
 * ApiBase::getVersion was removed (deprecated since 1.21).
 * ApiMain::getShowVersions was removed (deprecated in 1.21).
 * ApiMain::addModule was removed (deprecated in 1.21).
 * ApiMain::addFormat was removed (deprecated in 1.21).
 * ApiMain::getFormats was removed (deprecated in 1.21).
 * ApiPageSet::finishPageSetGeneration was removed (deprecated in 1.21).
 * ApiCreateAccount is deprecated, and will be removed soon.

Languages updated
MediaWiki supports over 350 languages.

Many localisations are updated regularly.

Below only new and removed languages are listed, as well as changes to languages because of Phabricator reports.


 * Change default numerals from Gurmukhi to Arabic for Punjabi locale.
 * Aliases of magic words in MessagesXx.php are sorted by usage.

Other changes

 * Added dependency injection (DI) infrastructure, see docs/injection.txt for details. It is planned to incrementally move MediaWiki code towards using DI, using the service locator (SL) pattern as a stepping stone.
 * ProfilerOutputUdp was removed. Note that there is a ProfilerOutputStats class.
 * WikiPage::doDeleteArticleReal and WikiPage::doDeleteArticle now ignore the 2nd and 3rd arguments (formerly $id and $commit).
 * Removed "loaderScripts" option from ResourceLoaderFileModule class.
 * Removed ORM-like wrapper added in 1.20.
 * LinkCache::getGoodLinks and LinkCache::getBadLinks were removed (deprecated in 1.26).
 * WikiPage::doQuickEdit was removed (deprecated since 1.21).
 * Removed SiteObject and SiteArray classes (deprecated in 1.21).
 * MessageBlobStore::getInstance was removed (deprecated since 1.25).
 * Free external links ("autolinked" urls) will now be terminated by  and HTML entity encodings of &nbsp, <, and >.
 * The default file revert message's timestamp is now in, instead of UTC.
 * The default name of the 'suppress' group page has been changed from 'Project:Oversight' to 'Project:Suppress'.
 * DatabaseBase::resultObject is now protected (use outside Database classes not necessary since 1.11).
 * Calling ResourceLoaderFileModule::readStyleFiles without a ResourceLoaderContext instance is deprecated.
 * ResourceLoader::getLessCompiler now takes an optional parameter of additional LESS variables to set for the compiler.
 * wfBaseConvert marked as deprecated, use Wikimedia\base_convert directly instead.
 * Obsolete maintenance scripts clearCacheStats.php and showCacheStats.php were removed. The underlying data is sent to StatsD (see ).
 * Removed msg_resource_links database table and associated code.
 * Removed msg_resource database table and associated code.
 * Skin::getNamespaceNotice was removed.
 * wfIsConfiguredProxy was removed (deprecated since 1.24).
 * wfDebugTimer was removed (deprecated since 1.25).
 * wfIsTrustedProxy was removed (deprecated since 1.24).
 * wfGetIP was removed (deprecated since 1.19).
 * MWHookException was removed.
 * OutputPage::appendSubtitle was removed (deprecated since 1.19).
 * OutputPage::loginToUse was removed (deprecated since 1.19).
 * Article::loadContent was removed (deprecated since 1.19).
 * User::editToken was removed (deprecated since 1.19).
 * Removed --force-normal option of dumpBackup.php, as it no longer served any useful purpose since 1.22.
 * The functions processOption and processArgs on the BackupDumper and TextPassDumper classes have been removed.
 * The maintenance/backupTextPass.inc file was deleted. You should include maintenance/dumpTextPass.php instead.
 * WikiPage::getUsedTemplates was removed (deprecated since 1.19).
 * wfEmptyMsg was removed (deprecated since 1.18).
 * OutputPage::permissionRequired was removed (deprecated since 1.18).
 * OutputPage::blockedPage was removed (deprecated since 1.18).
 * User::getSkin was removed (deprecated since 1.18).
 * OutputPage::includeJQuery was removed (deprecated since 1.17).
 * WikiPage::updateRestrictions was removed (deprecated since 1.19).
 * WikiPage::testPreSaveTransform was removed (deprecated since 1.19).
 * LogPage::logName was removed (deprecated since 1.19).
 * LogPage::logHeader was removed (deprecated since 1.19).
 * wfCheckLimits was removed (deprecated since 1.24).
 * Linker::makeKnownLinkObj was removed (deprecated since 1.16).
 * Linker::makeLinkObj was removed (deprecated since 1.16).
 * wfMsgForContentNoTrans was removed (deprecated since 1.18).
 * ChangesList::usePatrol was removed (deprecated since 1.22).
 * wfMsgNoTrans was removed (deprecated since 1.18).
 * Linker::makeImageLink2 was removed (deprecated since 1.20).
 * Title::userIsWatching was removed (deprecated since 1.20).
 * Removed WaitForSlave maintenance script; use SELECT MASTER_POS_WAIT database function directly instead.
 * wfMsg was removed (deprecated since 1.18).
 * wfMsgForContent was removed (deprecated since 1.18).
 * wfMsgReal was removed (deprecated since 1.18).
 * wfMsgGetKey was removed (deprecated since 1.18).
 * wfMsgHtml was removed (deprecated since 1.18).
 * wfMsgWikiHtml was removed (deprecated since 1.18).
 * wfMsgExt was removed (deprecated since 1.18).
 * Language::armourMath was removed (deprecated since 1.22).
 * LanguageConverter::armourMath was removed (deprecated since 1.22).
 * FakeConverter::armourMath was removed (deprecated since 1.22).
 * The unused jquery.validate ResourceLoader module was removed.
 * FileRepo::getRootUrl was removed (deprecated since 1.20).
 * User::generateToken was removed (deprecated since 1.20).
 * WikiPage::getRawText was removed (deprecated since 1.21).
 * ParserOutput::hasCustomDataUpdates was removed (deprecated since 1.25).
 * ParserOutput::addSecondaryDataUpdate was removed (deprecated since 1.25).
 * ParserOutput::getSecondaryDataUpdates was removed (deprecated since 1.25).
 * Gallery images with multiple caption pipes no longer concatenate them all together but instead pick the final one, similar to image syntax.
 * XML-like parser tags (such as ), when unclosed, will be left unparsed rather than consume everything until the end of the page.
 * New maintenance script resetUserEmail.php allows sysadmins to reset user emails in case a user forgot password/account was stolen.
 * wfCheckEntropy was removed (deprecated in 1.27).
 * Browser support for Internet Explorer 8 lowered from Grade A to Grade C.
 * ContentHandler::supportsCategories method added. Default is true. CategoryMembershipChangeJob updates are skipped for content that does not support categories.
 * wikidiff difference engine is no longer supported, anyone still using it are encouraged to upgrade to wikidiff2 which is actively maintained and has better package availability.
 * Database logic was removed from WatchedItem and a WatchedItemStore was created:
 * WatchedItem::IGNORE_USER_RIGHTS and WatchedItem::CHECK_USER_RIGHTS were deprecated. User::IGNORE_USER_RIGHTS and User::CHECK_USER_RIGHTS were introduced.
 * WatchedItem::fromUserTitle was deprecated in favour of the constructor.
 * WatchedItem::resetNotificationTimestamp was deprecated.
 * WatchedItem::batchAddWatch was deprecated.
 * WatchedItem::addWatch was deprecated.
 * WatchedItem::removeWatch was deprecated.
 * WatchedItem::isWatched was deprecated.
 * WatchedItem::duplicateEntries was deprecated.
 * EmailNotification::updateWatchlistTimestamp was deprecated.
 * User::getWatchedItem was removed.
 * Unit tests don't work with external PHPUnit anymore, Composer is now the only supported way. Run `composer install` to install it and other dev dependencies to run unit tests.
 * wl_id field added to the watchlist table.
 * Revision::getRawText was removed (deprecated since 1.21).
 * WikiPage::replaceSection was removed (deprecated since 1.21).
 * Article::replaceSection was removed (deprecated since 1.21).
 * Language::getLangObj was removed (deprecated since 1.24).
 * Language::getLanguageName was removed (deprecated since 1.20).
 * Language::getLanguageNames was removed (deprecated since 1.20).
 * Language::getTranslatedLanguageNames was removed (deprecated since 1.20).
 * Language::specialPage was removed (deprecated since 1.24).
 * MediaWikiTestCase::assertException was removed (deprecated since 1.22).
 * OutputPage::getHeadItems was removed (deprecated since 1.24).
 * OutputPage::getScript was removed (deprecated since 1.24).
 * OutputPage::out was removed (deprecated since 1.22).
 * OutputPage::setAllowedModules was removed (deprecated since 1.24).
 * UserrightsPage::makeGroupNameListForLog was removed (deprecated since 1.21).
 * MediaWikiSite::newFromGlobalId was removed (deprecated since 1.21).
 * Title::newFromRedirect was removed (deprecated since 1.21).
 * Skin::commonPrintStylesheet was removed (deprecated since 1.22).
 * Skin::getCommonStylePath was removed (deprecated since 1.24).
 * Skin::newFromKey was removed (deprecated since 1.24).
 * Skin::getUsableSkins was removed (deprecated since 1.23).
 * LoadBalancer::pickRandom was removed (deprecated in 1.21).
 * Article::getUndoText and WikiPage::getUndoText were removed (deprecated since 1.21).
 * DifferenceEngine::setText was removed (deprecated in 1.21).
 * Title::newFromRedirectArray was removed (deprecated in 1.21).
 * UserMailer::send no longer accepts $replyto as the 5th argument and $contentType as the 6th. These must be passed in the options array now.
 * Title::newFromRedirectRecurse was removed (deprecated in 1.21).
 * Skin::accesskey was removed (deprecated since 1.21).
 * Skin::blockLink was removed (deprecated since 1.21).
 * Skin::buildRollbackLink was removed (deprecated since 1.21).
 * Skin::emailLink was removed (deprecated since 1.21).
 * Skin::formatComment was removed (deprecated since 1.21).
 * Skin::formatHiddenCategories was removed (deprecated since 1.21).
 * Skin::formatLinksInComment was removed (deprecated since 1.21).
 * Skin::formatRevisionSize was removed (deprecated since 1.21).
 * Skin::formatSize was removed (deprecated since 1.21).
 * Skin::formatTemplates was removed (deprecated since 1.21).
 * Skin::generateTOC was removed (deprecated since 1.21).
 * Skin::getInternalLinkAttributes was removed (deprecated since 1.21).
 * Skin::getInternalLinkAttributesObj was removed (deprecated since 1.21).
 * Skin::getInterwikiLinkAttributes was removed (deprecated since 1.21).
 * Skin::getInvalidTitleDescription was removed (deprecated since 1.21).
 * Skin::getLinkColour was removed (deprecated since 1.21).
 * Skin::getRevDeleteLink was removed (deprecated since 1.21).
 * Skin::getRollbackEditCount was removed (deprecated since 1.21).
 * Skin::makeBrokenImageLinkObj was removed (deprecated since 1.21).
 * Skin::makeCommentLink was removed (deprecated since 1.21).
 * Skin::makeExternalImage was removed (deprecated since 1.21).
 * Skin::makeExternalLink was removed (deprecated since 1.21).
 * Skin::makeHeadline was removed (deprecated since 1.21).
 * Skin::makeImageLink was removed (deprecated since 1.21).
 * Skin::makeMediaLinkFile was removed (deprecated since 1.21).
 * Skin::makeMediaLinkObj was removed (deprecated since 1.21).
 * Skin::makeSelfLinkObj was removed (deprecated since 1.21).
 * Skin::makeThumbLink2 was removed (deprecated since 1.21).
 * Skin::makeThumbLinkObj was removed (deprecated since 1.21).
 * Skin::normaliseSpecialPage was removed (deprecated since 1.21).
 * Skin::normalizeSubpageLink was removed (deprecated since 1.21).
 * Skin::processResponsiveImages was removed (deprecated since 1.21).
 * Skin::revComment was removed (deprecated since 1.21).
 * Skin::revDeleteLink was removed (deprecated since 1.21).
 * Skin::revDeleteLinkDisabled was removed (deprecated since 1.21).
 * Skin::revUserLink was removed (deprecated since 1.21).
 * Skin::revUserTools was removed (deprecated since 1.21).
 * Skin::specialLink was removed (deprecated since 1.21).
 * Skin::splitTrail was removed (deprecated since 1.21).
 * Skin::titleAttrib was removed (deprecated since 1.21).
 * Skin::tocIndent was removed (deprecated since 1.21).
 * Skin::tocLine was removed (deprecated since 1.21).
 * Skin::tocLineEnd was removed (deprecated since 1.21).
 * Skin::tocList was removed (deprecated since 1.21).
 * Skin::tocUnindent was removed (deprecated since 1.21).
 * Skin::tooltip was removed (deprecated since 1.21).
 * Skin::tooltipAndAccesskeyAttribs was removed (deprecated since 1.21).
 * Skin::userTalkLink was removed (deprecated since 1.21).
 * Skin::userToolLinksRedContribs was removed (deprecated since 1.21).
 * wikidiff3 is now the default and only PHP diff engine. It provides improved diff performance on complex changes. = 'wikidiff3' therefore makes no difference now. Users are still recommended to use wikidiff2 if possible, though.
 * User::addNewUserLogEntry was deprecated.
 * User::addNewUserLogEntryAutoCreate was deprecated.
 * User::isPasswordReminderThrottled was deprecated.
 * Bot-oriented parameters to Special:UserLogin (wpCookieCheck, wpSkipCookieCheck) were removed.
 * Installer can now be customized without patching MediaWiki code, see mw-config/overrides/README for details.

Compatibility
MediaWiki 1.27 requires PHP 5.5.9 or later.

There is experimental support for HHVM 3.6.5 or later.

MySQL is the recommended DBMS.

PostgreSQL or SQLite can also be used, but support for them is somewhat less mature.

There is experimental support for Oracle and Microsoft SQL Server.

The supported versions are:


 * MySQL 5.0.3+
 * PostgreSQL 8.3+
 * SQLite 3.3.7+
 * Oracle 9.0.1+
 * Microsoft SQL Server 2005 (9.00.1399)

Upgrading
1.27 has several database changes since 1.26, and will not work without schema updates. Note that due to changes to some very large tables like the revision table, the schema update may take quite long (minutes on a medium sized site, many hours on a large site).

If upgrading from before 1.11, and you are using a wiki as a commons repository, make sure that it is updated as well. Otherwise, errors may arise due to database schema changes.

If upgrading from before 1.7, you may want to run refreshLinks.php to ensure new database fields are filled with data.

If you are upgrading from MediaWiki 1.4.x or earlier, you should upgrade to 1.5 first. The upgrade script maintenance/upgrade1_5.php has been removed with MediaWiki 1.21.

Don't forget to always back up your database before upgrading!

See the file UPGRADE for more detailed upgrade instructions.

For notes on 1.26.x and older releases, see HISTORY.

Online documentation
Documentation for both end-users and site administrators is available on MediaWiki.org, and is covered under the GNU Free Documentation License (except for pages that explicitly state that their contents are in the public domain):

https://www.mediawiki.org/wiki/Documentation

Mailing list
A mailing list is available for MediaWiki user support and discussion:

https://lists.wikimedia.org/mailman/listinfo/mediawiki-l

A low-traffic announcements-only list is also available:

https://lists.wikimedia.org/mailman/listinfo/mediawiki-announce

It's highly recommended that you sign up for one of these lists if you're going to run a public MediaWiki, so you can be notified of security fixes.

IRC help
There's usually someone online in #mediawiki on irc.freenode.net.