Issue #2930407 by tstoeckler, lauriii, alexpott: Allow specifying summary attributes for details elements

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 #2346773 by dmsmidt, lokapujya, klakegg, marcvangend, andrewmacpherson, ptsimard, Getekid, Rade, yoroy, tstoeckler, mgifford, tim.plunkett, estoyausente, xjm, PierreMarcel, hass, SKAUGHT, sukanya.ramakrishnan, flyke, alvar0hurtad0, bojanz, pwolanin, arunkumark, Bojhan, bleen: Details form element should open when there are errors on child elements

Issue #2709411 by dagmar, jhodgdon: t() is used in an inconsistent way on Drupal\Core\Render\Element documentation

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