+* As part of work to modernise user-generated content clean-up, a config option and some
+ methods related to HTML validity were removed without deprecation. The public methods
+ MWTidy::checkErrors() and its callee TidyDriverBase::validate() are removed, as are
+ MediaWikiTestCase::assertValidHtmlSnippet() and ::assertValidHtmlDocument(). The
+ $wgValidateAllHtml configuration option is removed and will be ignored.
+* Execution of external programs using MediaWiki\Shell\Command now applies RESTRICT_DEFAULT
+ Firejail restriction by default.
+* The ResourceLoaderModule::getHashMtime() and ::getDefinitionMtime() methods,
+ deprecated in 1.26, were removed.