While working on T216348 I have found an issue with message recentchanges-legend-watchlistexpiry
$legend .= Html::rawElement( 'dd', [ 'class' => 'mw-changeslist-legend-watchlistexpiry', 'id' => $watchlistLabelId ], $context->msg( 'recentchanges-legend-watchlistexpiry' )->text() );
The combination of Html::rawElement and Message::text leads to XSS leaks
The message was added with 1.35 and is behind a feature flag ($wgWatchlistExpiry)
Should use Html::element or Message::parse/Message::escaped, not sure.