Hi, As part of the goal to have MediaWiki 1.31 default to using RemexHtml and replacing tidy, we want to remove MWTidy::checkErrors() and $wgValidateAllHtml as part of MediaWiki 1.31, without a deprecation period. MWTidy::checkErrors() basically ran the provided input through tidy, and checked if it complained. This doesn't make sense using an HTML 5 parser, since they provide recovery conditions to fix parse errors. If $wgValidateAllHtml was set, MediaWiki would output an error page instead of the content if tidy reported errors in the output. Technically, this also means removing TidyDriverBase::validate() (unused besides MWTidy::checkErrors()), and MediaWikiTestCase::assertValidHtmlDocument/assertValidHtmlSnippet() (now unused; previously only used in Capiunto as a defensive check). There is some more rationale and discussion on the task for this: [2]. The Gerrit patch is [3]. [1] https://phabricator.wikimedia.org/T185753 [2] https://phabricator.wikimedia.org/T191670 [3] https://gerrit.wikimedia.org/r/#/c/425093/ -- James & Legoktm