Issue #2853503 by Aki Tendo, alexpott, larowlan, Wim Leers, klausi, fgm, dawehner, mondrake, catch, Berdir, neclimdul, borisson_: Remove all assert('string') calls from Drupal core because deprecated in PHP 7.2

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 #2716685 by Mile23: Part 2: Fix several errors in the 'Drupal.Commenting.DocComment' coding standard

Issue #2572693 by Mile23, andriyun, andypost, attiks: Fix 'Drupal.ControlStructures.ControlSignature' coding standard

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 #2430397 by Wim Leers, Fabianx: When mapping cache contexts to cache keys, include the cache context ID for easier debugging

Issue #2512866 by lauriii, Berdir, Wim Leers, Fabianx, effulgentsia, catch, dawehner: CacheContextsManager::optimizeTokens() optimizes ['user', 'user.permissions'] to ['user'] without adding cache tags to invalidate that when the user's roles are modified

Issue #2483781 by borisson_, rbayliss, cilefen, mitalimehta, joshi.rohit100: Move cache contexts classes from \Drupal\Core\Cache to \Drupal\Core\Cache\Context

Issue #2468151 by lhangea, rpayanm, Palashvijay4O: Rename the CacheContexts service to CacheContextsManager

Issue #2457887 by prateekMehta, stefan.r, rpayanm, alexpott: Use Utility\SafeMarkup class instead of Utility\String for placeholder(), checkPlain(),format() functions

Issue #2451679 by Wim Leers, dawehner: Validate cache contexts (+ cache contexts in some views plugins wrong)

Issue #2432837 by Wim Leers, Fabianx: Make cache contexts hierarchical (e.g. 'user' is more specific than 'user.roles')

Issue #2329101 by Wim Leers: CacheableInterface only has a getCacheKeys() method, no getCacheContexts(), leads to awkward implementations

Issue #2158003 by Wim Leers, msonnabaum, effulgentsia, moshe weitzman: Remove Block Cache API in favor of blocks returning #cache with cache tags.