Issue #2873696 by nvexler, wengerk, gido, Jo Fitzgerald, xjm: Add @internal to core classes, methods, properties to Form Classes

Issue #2776975 by joelpittet, dawehner, tim.plunkett, xjm, pfrenssen: March 3, 2017: Convert core to array syntax coding standards for Drupal 8.3.x RC phase

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

Issue #2502621 by Pravin Ajaaz, hussainweb, Peacog, jhodgdon, ivanjaros: Replace implement notes with inheritdoc tag

Issue #2570355 by Sutharsan, stefan.r, kgoel, josephdpurcell, joelpittet, justAChris, dawehner, pfrenssen, pwolanin, David_Rothstein, catch: Replace remaining !placeholder and @placeholder with :placeholder for URLs

Issue #2403229 by robertdbailey, andypost, penyaskito, Gábor Hojtsy: language.negotiation configuration can have overrides bleed in

Issue #2470307 by Mark_L6n, eiriksm, Gábor Hojtsy: Modifying path prefix for URL language detection causes error message for default language

Issue #2422685 by balagan: Language negotiation configuration page titles inconsistent, should not even mention "negotiation"

Issue #2411343 by pcambra: Only allowing to have empty language path prefix for the default language is inappropriate

Issue #2392319 by alexpott, effulgentsia: Config objects (but not config entities) should by default be immutable

Issue #2328293 by keopx, JeroenT, ianthomas_uk, ashutoshsngh, rpayanm, hudo, a_thakur: Remove usage of language_list()

Issue #2341341 by YesCT, martin107, vijaycs85, fran seva: Change public 'name' property access on languages to getName() and add back setName().

Issue #2340667 by YesCT, Pedro Lozano, alexpott, martin107: Protect Drupal\Core\Language\Language::id, and use getId().

Issue #2343943 by marcus7777, pp, alimac, pefferen | Greg Sims: Fixed Language domain may not be left blank for default language.

Issue #2339435 by YesCT, alexpott: Default no longer needs to be a property on Language or ConfigurableLanguage.

Issue #2308821 by tim.plunkett: Replace FormErrorInterface with $form_state->setErrorByName() and $form_state->setError().

Issue #2239065 by tim.plunkett | webchick: Overridden config bleeding through to configuration forms.

Issue #1862202 by plach, Berdir, katbailey, ParisLiakos, alexpott, chx, sun, larowlan, Gábor Hojtsy, cosmicdreams, vijaycs85, YesCT, penyaskito, andypost, Albert Volkman, joelpitett: Objectify the language system.

Issue #2145007 by tim.plunkett, h3rj4n: Convert form_set_error() in FormBase classes to use FormErrorInterface.

Issue #2089627 by tim.plunkett: Move \Drupal\system\SystemConfigFormBase to \Drupal\Core\Form\ConfigFormBase.

Issue #1754246 by webflo, swentel, penyaskito, andypost, alexpott, YesCT, dagmar: Languages should be configuration entities.