tried version 2.0 for the first time om MW 1.31 and get this error
[X@CRKp0hUbgJtA6mJBGcLAAAAA8] /User:Admin Error from line 239 of ..extensions/HeaderTabs/includes/HeaderTabs.php: Class 'OOUI\TabPanelLayout' not found
Backtrace:
#0 ../extensions/HeaderTabs/includes/HeaderTabsHooks.php(47): HeaderTabs::replaceFirstLevelHeaders(Parser, string, array)
#1 ..includes/Hooks.php(177): HeaderTabsHooks::replaceFirstLevelHeaders(Parser, string)
#2 ../includes/Hooks.php(205): Hooks::callHook(string, array, array, NULL)
#3 ../includes/parser/Parser.php(1428): Hooks::run(string, array)
#4 ../includes/parser/Parser.php(446): Parser->internalParseHalfParsed(string, boolean, boolean)
#5 ../includes/content/WikitextContent.php(323): Parser->parse(string, Title, ParserOptions, boolean, boolean, integer)
#6 ../includes/content/AbstractContent.php(516): WikitextContent->fillParserOutput(Title, integer, ParserOptions, boolean, ParserOutput)
#7 ../includes/poolcounter/PoolWorkArticleView.php(144): AbstractContent->getParserOutput(Title, integer, ParserOptions)
#8 ../includes/poolcounter/PoolCounterWork.php(123): PoolWorkArticleView->doWork()
#9 ../includes/page/Article.php(604): PoolCounterWork->execute()
#10 ../includes/actions/ViewAction.php(68): Article->view()
#11 ../includes/MediaWiki.php(500): ViewAction->show()
#12 ../includes/MediaWiki.php(294): MediaWiki->performAction(Article, Title)
#13 ../includes/MediaWiki.php(818): MediaWiki->performRequest()
#14 ../includes/MediaWiki.php(524): MediaWiki->main()
#15 ../index.php(42): MediaWiki->run()
#16 {main}