RELEASE-NOTES-1.27

== MediaWiki 1.27.1 ==

This is a 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 <style> 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()

== MediaWiki 1.27 ==

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

=== Configuration changes in 1.27 ===
* $wgAllowMicrodataAttributes and $wgAllowRdfaAttributes were removed,
  now always enabled. If you use RDFa on your wiki, you now have to explicitly
  set $wgHtml5Version to 'HTML+RDFa 1.0' or 'XHTML+RDFa 1.0'.
* $wgUseLinkNamespaceDBFields was removed.
* Deprecated $wgResourceLoaderMinifierStatementsOnOwnLine and
  $wgResourceLoaderMinifierMaxLineLength, 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.
* $wgDebugDumpSqlLength was removed (deprecated in 1.24).
* $wgDebugDBTransactions was removed (deprecated in 1.20).
* $wgUseXVO 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 $wgUseKeyHeader that provides similar
  functionality but instead of the MediaWiki-specific X-Vary-Options header,
  uses the draft Key header standard.
* $wgScriptExtension (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.
* $wgMaxSquidPurgeTitles was removed.
* $wgAjaxWatch was removed. This is now enabled by default.
* $wgUseInstantCommons 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 $wgForeignFileRepos documentation for tweaks.
* (T27397) WebP is enabled by default as an uploadable filetype.
* (T48998) $wgArticlePath must now be either a full url, or start with a "/".
* $wgRateLimitLog was removed; use $wgDebugLogGroups['ratelimit'] instead.
* Deprecated API formats dbg, txt, and yaml have been removed.
* CLDRPluralRule* classes have been replaced with
  wikimedia/cldr-plural-rule-parser.
* Removed $wgProfilePerHost, $wgUDPProfilerHost, $wgUDPProfilerPort,
  $wgUDPProfilerFormatString, $wgStatsMethod, $wgAggregateStatsID,
  $wgStatsFormatString, and $wgProfileCallTree (deprecated since 1.20).
* For proper operation of LocalIdLookup with shared user tables, ensure that
  $wgSharedDB and $wgSharedTables are properly set even on the "central" wiki
  that all others are sharing from and that $wgLocalDatabases is set to the
  full list of sharing wikis on all those wikis.
* Massive overhaul to session handling:
** $wgSessionsInObjectCache is no longer supported and must be true, due to
   MediaWiki\Session\SessionManager. $wgSessionHandler is similarly no longer
   used.
** ObjectCacheSessionHandler is removed, replaced with
   MediaWiki\Session\PhpSessionHandler.
** PHP session handling in general ($_SESSION, session_id(), and so on) is
   deprecated. Use MediaWiki\Session\SessionManager instead. A new config
   variable, $wgPHPSessionHandling, 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.
* $wgAllowAsyncCopyUploads 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.
* $wgEnotifUseJobQ 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.
* $wgPreloadJavaScriptMwUtil was removed (deprecated in 1.26).
  Extensions, skins, gadgets and scripts that use the mediawiki.util module must
  express a dependency on it.
* $wgIncludeLegacyJavaScript, 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 $wgCopyrightIcon (deprecated since 1.18). Use
  $wgFooterIcons['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 $wgSessionInsecureSecrets = 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.
** $wgRequirePasswordforEmailChange is removed.
* $wgWellFormedXml has been removed.

=== New features in 1.27 ===
* $wgDataCenterUpdateStickTTL 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.
* $wgCdnMaxageLagged 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 $wgLBFactoryConf.
* 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.
* $wgAPIMaxLagThreshold 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
  $wgLocaltimezone 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.
* $wgMaxUserDBWriteDuration 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.
* $wgCdnReboundPurgeDelay was added to provide secondary delayed purges of URLs
  from CDN to mitigate DB replication lag and WAN cache purge lag.
* (T49162) 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 $wgUseFilePatrol.
* 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 $wgGrantPermissions and
  $wgGrantPermissionGroups 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) $wgMWOAuthGrantPermissions and
   $wgMWOAuthGrantPermissionGroups.
* 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.
* $wgContentHandlers now also supports callbacks to create an instance of the
  appropriate ContentHandler subclass.
* Added $wgAuthenticationTokenVersion, 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.
* $wgEventRelayerConfig 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.
* (T33313) Add a preference for watching uploads by default, also applies
  to API-based upload tools.
* $wgJpegPixelFormat 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 $wgAuthManagerConfig.
** 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, $wgChangeCredentialsBlacklist and $wgRemoveCredentialsBlacklist
   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 $wgUploadDialog.

=== External library changes in 1.27 ===

==== 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.

==== Removed and replaced external libraries ====

=== Bug fixes in 1.27 ===
* Special:Upload will now display correct maximum allowed file size when running
  under HHVM (T116347).
* (T54077) 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 in 1.27 ===
* 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.
* (T47988) 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 in 1.27 ===
* 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 in 1.27 ===

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.

* (T113688) Change default numerals from Gurmukhi to Arabic for Punjabi locale.
* (T116020) Aliases of magic words in MessagesXx.php are sorted by usage.

=== Other changes in 1.27 ===
* 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).
* (T84937) Free external links ("autolinked" urls) will now be terminated
  by &nbsp; and HTML entity encodings of &nbsp, <, and >.
* (T36948) The default file revert message's timestamp is now in
  $wgLocaltimezone, 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 $wgStatsdServer).
* 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 <gallery>), 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. $wgExternalDiffEngine = '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 or later
* PostgreSQL 8.3 or later
* SQLite 3.3.7 or later
* Oracle 9.0.1 or later
* 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.