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 #2340123 by Wim Leers: Setting cache tags can be tricky: use strings instead of nested arrays to improve DX.

Issue #2224847 by pwolanin, damiankloip, danblack, Berdir: Fixed Automatically shorten cid's in Cache\DatabaseBackend and PhpBackend.

Issue #2228261 by beejeebus, kim.pepper, alexpott, Wim Leers | catch: Add a local, PhpStorage-based cache backend.

Issue #2228261 by beejeebus, kim.pepper, alexpott, Wim Leers: Add a local, PhpStorage-based cache backend.

Issue #1167248 by Berdir, damiankloip, Alan Evans, beejeebus, catch: Add CacheBackendInterface::setMultiple().

Issue #2169447 by damiankloip, sun, longwave: DX: Supply CacheBackendInterface::CACHE_PERMANENT as Cache::PERMANENT.

Issue #1858616 by Berdir: Extract generic CacheCollector implementation and interface from CacheArray.

Issue #1167144 by chx, catch, claudiu.cristea: Make cache backends responsible for their own storage.

Issue #1808112 by sun: Fixed Missing method visibility, bogus phpDoc and coding style in Cache backend classes.

Issue #1393392 by c960657, fubhy: Convert prefix cache clears to cache tags, then remove support for them.