the "headelement" template key are no longer supported. Setting
$useHeadElement = false; is no longer supported and will not cause old keys
like "headlinks", "skinnameclass", etc. to be defined.
+* BREAKING CHANGE: The files commonElements.css, commonContent.css and
+ commonInterface.css (in skins/common/) have been removed. Skins may no longer
+ rely on their presence and include them in their style modules. ResourceLoader
+ modules introduced in MediaWiki 1.23 should be loaded instead:
+ - skins/common/commonElements.css → 'mediawiki.skinning.elements' module
+ - skins/common/commonContent.css → 'mediawiki.skinning.content' module
+ - skins/common/commonInterface.css → 'mediawiki.skinning.interface' module
* The deprecated 'SpecialVersionExtensionTypes' hook was removed.
* (bug 63891) Add 'X-Robots-Tag: noindex' header in action=render pages.
* SpecialPage no longer supports the syntax for invoking wfSpecial*() functions.