Issue #2568609 by alexpott: Replace remaining !placeholder for Non-URL HTML outputs only in theme functions in system.admin.inc

Issue #2501737 by sclapp, joelpittet, lauriii, cilefen, golddragon007, akalata: Remove SafeMarkup::set in theme_system_modules_details()

Issue #2056089 by BarisW, TR, mgifford, rodvolpe, Dom., nambisolo, nod_, katewelling, Manjit.Singh, jhodgdon, Bojhan, Wim Leers: UI problems on the Modules/Extend page

Issue #2489830 by cilefen, davidhernandez, dcmul, Adam Clarey, joshi.rohit100, rpayanm, sqndr, Cottser, lauriii: Improve theme compatibility error message

Issue #2506195 by alexpott, joelpittet, xjm, David_Rothstein, Fabianx, pwolanin: Remove SafeMarkup::set() from Xss::filter()

Issue #2392293 by bircher, tim.plunkett, alexpott, cilefen, gobinathm: Refactor hook_system_info_alter implementations to use ModuleUninstallValidatorInterface

Issue #2278017 by cilefen, bircher, effulgentsia: When a content entity type providing module is uninstalled, the entities are not fully deleted, leaving broken reference

Issue #1833932 by lauriii, lokapujya, cilefen, Cottser, joelpittet, jenlampton, iMiksu, lanchez, ericrdb, mikispeed, Eric_A, mikemiles86: Convert theme_system_compact_link() into a #type link

Issue #2324371 by lauriii, aneek, chx, joelpittet, webflo, Fabianx, rteijeiro: Fix common HTML escaped render #key values due to Twig autoescape.

Issue #2329851 by lanchez, lauriii, Jolidog | davidhernandez: Move miscellaneous system classes from preprocess to templates.

Issue #2277103 by tim.plunkett, pwolanin, Wim Leers, dawehner, hotpizzas: Switch Drupal::l() and LinkGenerator to expect a Url object.

Issue #2301317 by pwolanin, dawehner, Wim Leers, effulgentsia, YesCT, xjm, alexpott: MenuLinkNG part4: Conversion.

Revert "Issue #2301317 by pwolanin, effulgentsia, Wim Leers, dawehner, alexpott: MenuLinkNG part4: Conversion."

This reverts commit fd2db9cd.

Issue #2301317 by pwolanin, effulgentsia, Wim Leers, dawehner, alexpott: MenuLinkNG part4: Conversion.

Issue #1825952 by Fabianx, joelpittet, bdragon, heddn, chx, xjm, pwolanin, mikey_p, ti2m, bfr, dags, cilefen, scor, mgifford: Turn on twig autoescape by default

Issue #1987848 by disasm, ocsilalala, kim.pepper, pwieck, Cottser, pratik60, h3rj4n, pfrenssen, InternetDevels, ParisLiakos, rgoodine, tlyngej, vijaycs85, robeano: Convert system_theme_default() to a new style controller.

Issue #2089433 by ianthomas_uk, grom358, herom, thedavidmeister, visabhishek, longwave, Sweetchuck: Remove uses of deprecated XSS filter functions.

Issue #2100311 by killua99, yannickoo: Allow filtering of modules by arbitrary search strings on the uninstall page.

Issue #2075475 by sqndr, Oostie, meladawy, temaruk, LewisNyman: Theme with no screenshot causes CSS height issue.

Issue #2219617 by visabhishek, galooph, joshtaylor, Cottser: Remove @ingroup themeable from preprocess function docblocks.

Issue #2151095 by joelpittet, longwave, c4rl, IshaDakota, pplantinga, gnuget, jeanfei, sbudker1, Cottser: Convert theme_admin_page() to Twig

Sorry, wrong commit credit.

This reverts commit d1653fd0.

Issue #2151089 by longwave, joelpittet, c4rl, IshaDakota, pplantinga, gnuget, jeanfei, sbudker1, Cottser: Convert theme_admin_block() to Twig.

Issue #2171071 by jessebeach, dawehner, chakrapani, longwave, Gábor Hojtsy, xjm, Wim Leers: Rename drupal_add_library() to _drupal_add_library() and remove its uses.

Issue #2210197 by sun, longwave, Sutharsan: Remove public access to Extension::$type, ::$name, ::$filename.

Issue #2151119 by joelpittet, InternetDevels, jamesrutherford, Cottser, idflood, c4rl, IshaDakota, pplantinga, gnuget, longwave, jeanfei, sbudker1: Convert theme_system_themes_page() to Twig.

Revert "Issue #2210197 by sun, longwave: Remove public access to Extension::$type, ::$name, ::$filename." Broke 'drush en simpletest' on testbots

This reverts commit 2c51074d.