Issue #2665992 by alexpott, klausi, heykarthikwithu, xjm, tstoeckler: @file is not required for classes, interfaces and traits

Issue #2557519 by alexpott, joelpittet: Remove many usages SafeMarkup::checkPlain() and replace with Html::escape()

Issue #2550467 and #2120113 by alexpott, manningpete, akalata, nlisgo, nod_, harjotsingh: Remove #value_prefix and #value_suffix from HtmlTag

Issue #2506581 by alexpott, Wim Leers, Fabianx, xjm, joelpittet, Cottser, dawehner: Remove SafeMarkup::set() from Renderer::doRender

Issue #1392754 by tss, justAChris, jhodgdon: Comply with new documentation standards for @file for namespaced class files

Issue #2511472 by Wim Leers, Fabianx, dawehner: Refactor all usages of drupal_render()/Renderer::render() that break #2450993

Issue #2457887 by prateekMehta, stefan.r, rpayanm, alexpott: Use Utility\SafeMarkup class instead of Utility\String for placeholder(), checkPlain(),format() functions

Issue #552478 by markcarver, sun, effulgentsia, jhedstrom, ohnobinki: Restrict "self-closing" tags to only void elements in drupal_pre_render_html_tag

Issue #2364157 by mpdonadio, dawehner, martin107, Berdir, pcambra, naveenvalecha, tim.plunkett: Replace most existing _url calls with Url objects

Issue #2347999 by Mile23, daffie, cs_shadow, cosmicdreams: DrupalUnitTestBase is deprecated, replace with KernelTestBase

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 #2347465 by tim.plunkett, dawehner, cilefen: Convert all instances of #type link/links to convert to use routes.

Issue #2343661 by larowlan, tim.plunkett | xjm: Rename l() to _l() and url() to _url(), and document replacements.

Issue #2031301 by andypost, Cottser, xjm, mark.labrecque, mariacha1, joelpittet, robynlgreen, danquah, trogels, Eric_A, thedavidmeister, jenlampton: Replace theme_more_link() and replace with #type 'more_link'.

Issue #2304399 by er.pushpinderrana, undertext | samuel.mortenson: Fixed "class" attribute in drupal_render should be an array.

Issue #697760 by sun: Replace getInfo() in tests with native phpDoc + annotations (following PHPUnit).

Issue #1067408 by alexpott, Jalandhar, jessebeach, Désiré, neetu morwani, dawehner, sun: Themes do not have an installation status.

Revert "Issue #2218039 by sun, dawehner: Render the maintenance/install page like any other HTML page."

Broke update.php.

This reverts commit 10b03890.

Issue #2203407 by nod_, sun: Replace #attached library array values with provider-namespaced strings.

Issue #2152203 by joelpittet, InternetDevels, rteijeiro,  steveoliver, hussainweb, shanethehat, jenlampton, kpa, AnythonyR, EVIIILJ, kgoel, Cottser, dsdeiz, hanpersand: Convert theme_container() to Twig.

Issue #1996238 by sun, nod_, damiankloip, Wim Leers, longwave, alexpott, Xano, mdrummond, Mark Carver, Jeff Burnz, highrockmedia, joelpittet, et al: Replace hook_library_info() by *.libraries.yml file.

Issue #2072647 by thedavidmeister, herom, jwilson3, Cottser, LinL: #theme 'maintenance_page' should support render arrays in #content.

Issue #2058761 by thedavidmeister: PHP notice when #attributes is not set with #theme_wrappers() 'container'.