Issue #3106216 by Spokje, longwave, alexpott, apaderno, Hardik_Patel_12, daffie: Remove unused variables from core

Issue #2935256 by Jo Fitzgerald, voleger, kim.pepper, ibustos, Yogesh Pawar, catch, jibran: Remove all usages of drupal_get_message and drupal_set_message in modules

Issue #2857857 by vegantriathlete, Jo Fitzgerald, snehi, plach, xjm, Skabbkladden: Check use of "it's" in core to ensure proper use

Issue #2754977 by dmsmidt, marcvangend, mohit_aghera, Getekid, tim.plunkett, ndf: Enhance formErrorHandler to include children errors on RenderElements

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

Issue #2578561 by tim.plunkett, joelpittet, Bojhan, Fabianx, xjm, cilefen, David_Rothstein, DamienMcKenna: Move "Inline Form Errors" functionality to optional module and restore D7-style form errors by default

Issue #2550981 by alexpott, stefan.r, davidhernandez, joelpittet, Wim Leers, xjm, josephdpurcell, akalata, dawehner: Remove SafeMarkup::set in FormErrorHandler::displayErrorMessages()

Issue #1493324 by tim.plunkett, dmsmidt, mgifford, bleen18, davidhernandez, crasx, mparker17, stefan.r, YesCT, joelpittet, tstoeckler, larowlan, vijaycs85, swentel, rpayanm, Bojhan, LewisNyman, emma.maria, BarisW, njbarrett, rteijeiro, nod_, sun, joshtaylor, mrjmd, webchick, marcvangend, kattekrab, SKAUGHT, bowersox, andrewmacpherson, Manjit.Singh, RavindraSingh, Wim Leers, BLadwin, aspilicious, mortendk, mausolos, jessebeach, Gábor Hojtsy, anandps, falcon03, franz, andypost, rooby, rootwork, Cottser, Xano: Inline form errors for accessibility and UX