Issue #2089331 by grom358 | thedavidmeister: [meta] Replace calls to check_plain() with Drupal\Component\Utility\String::checkPlain().
Issue #2080343 by connork, izus, rahul.shinde, lokapujya | mrsinguyen: Remove Unused local variables from system module.
Issue #2052473 by ricky.middaugh, lokapujya, Jalandhar, mgifford, jessebeach, BarisW, falcon03: Add aria-label or aria-describedby attributes to all <nav> elements.
Issue #2250325 by jhodgdon, azinck, splatio: Fixed Route book.render (path /book) does not seem to work.
Issue #1898420 by mondrake, joelpittet, InternetDevels, claudiu.cristea, c4rl, DamienMcKenna, Albert Volkman, shanethehat, thedavidmeister: Image.module - Convert theme_ functions to Twig.
Issue #2151821 by joelpittet, JacobSanford, jjcarrion, rteijeiro, c4rl, IshaDakota, pplantinga, gnuget, longwave, jeanfei, sbudker1: Convert theme_system_config_form() to Twig