Issue #2557299 by alexpott, Manuel Garcia, borisson_, phenaproxima, swentel, Berdir, larowlan, mbovan, martin107, LKS90, segi, tim.plunkett, giancarlosotelo: Any AJAX call disregards machine name verification when AJAX is used and leads to a fatal error

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

SA-CORE-2016-005 by larowlan, xjm, David_Rothstein, Dave Reid, Crell, cilefen, alexpott, mlhess, catch, pwolanin, YesCT, dawehner, quicksketch, Heine, znerol, charlotte.b, jnicola, ezraw

(cherry picked from commit c5da97f9)

Issue #2713831 by vegantriathlete, lisa.ugray, joshi.rohit100, jhodgdon, deviantintegral, kellyimagined, alexpott, akalata, soulsesa: Document #machine_name exists parameters

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

Issue #2560137 by dawehner, pwolanin, klausi, tsphethean, sun: Posting an array as value of a form element is allowed even when a string is expected (and bypasses #maxlength constraints) - first step: text fields

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

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

Issue #2335659 by tim.plunkett, dawehner, effulgentsia, sun: Remove FormState ArrayAccess usage from core.