Issue #2808233 by gnuget, dawehner, Wim Leers, tedbow, Chi, dysrama: REST 403 responses don't tell the user *why* access is not granted: requires deep Drupal understanding to figure out

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

Issue #2454649 by Aki Tendo, dawehner: Cache Optimization and hardening -- [PP-1] Use assert() instead of exceptions in Cache::merge(Tags|Contexts)

Issue #2526326 by borisson_, Berdir, Wim Leers, Xano: Update CacheableMetadata & AccessResult to use RefinableCacheableDependency(Interface|Trait)

Issue #2428703 by Wim Leers: Add a 'user.permissions' cache context (was: "Should cache contexts be able to associate a cache tag?")

Issue #1986640 by Wim Leers, chx, dawehner, effulgentsia: Support AND/OR conjunctions for permission checks.