Issue #2481453 by dawehner, pwolanin, rteijeiro, neclimdul, znerol: Implement query parameter based content negotiation as alternative to extensions

Issue #2368987 by Wim Leers, Berdir, Schnitzel, epari.siva, bircher, vijaycs85, likin: Move internal page caching to a module to avoid relying on config get on runtime

Issue #2472281 by pwolanin: 404/403 responses for non-existing nodes are cached in Page Cache/reverse proxy, are not invalidated when the node is created

Issue #2467041 by mr.baileys, jan.stoeckler: max-age on HTML responses wrongly set to `max-age=0, private` instead of `max-age=N, public` (breaks reverse proxies and client-side caching)

Issue #2464659 by Wim Leers, rteijeiro: Routes that are varied by the 'user.permissions' cache context for anonymous users must also get the anonymous Role's cache tag

Issue #2040135 by Wim Leers, Berdir: Caches dependent on simple config are only invalidated on form submissions

Issue #2395395 by alexpott, effulgentsia, Gábor Hojtsy: TestBase lacks a config method to be used consistently in tests

Issue #2350823 by lauriii, jhedstrom, Tim Bozeman, cilefen, davidhernandez, inqui, Cottser, xjm: Use the Classy theme in the Testing profile

Issue #2340251 by iMiksu, alexpott, tim.plunkett, dawehner, Wim Leers: Remove most remaining url() calls.

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

Issue #697760 by sun: Replace getInfo() in tests with native phpDoc + annotations (following PHPUnit).

Issue #2124957 by Wim Leers, catch: Replace 'content' cache tag with 'rendered' and use it sparingly.

Issue #2257709 by znerol, Wim Leers: Remove the interdependence between the internal page cache and management of the Cache-Control header for external caches.

Issue #2185617 by Wim Leers, voidberg, drifter: Each page cache entry should have a theme cache tag.

Issue #2217371 by Wim Leers: Expose cache tags to reverse proxies: X-Drupal-Cache-Tags header (by just slightly changing an existing header).

Issue #2167039 by likin, dawehner, Wim Leers, tstoeckler, vijaycs85: Regression: page cache tags broken, also: some routes incorrectly use _controller -> No page object in template variables -> Fatal in seven_preprocess_page().

Issue #1957142 follow-up by dawehner, jibran: Fix a few more config() => Drupal::config() stragglers.

Issue #1476810 by Spleshka, franz: Fixed drupal_serve_page_from_cache() can serve uncompressed data with Content-Encoding gzip header with page_cache_without_database = 1.

Issue #1855260 by beejeebus, msonnabaum, larowlan: Fixed Page caching broken by accept header-based routing.

Issue #1984766 by sdboyer, Niklas Fiekas, msonnabaum: Fixed Start relying on Request/Response objects for cache handling.

Issue #2004908 by sdboyer: Added Allow tests to specify that response headers should be dumped in verbose mode.

Issue #1853086 by katbailey, msonnabaum, alexpott: Remove cache.page.enabled in favor of an explicit internal cache setting.

Issue #1431658 by Albert Volkman, xjm, kid_icarus, ChinggizKhan, rgristroph, connork: Massive API docs cleanup for system tests

Issue #1669902 by alexpott, aspilicious, sun: Adjust system.performance configuration for new guidelines.

Issue #1711070 by kid_icarus, tim.plunkett, xjm, droplet, zendoodles and cam8001: Convert tests to use ::$modules property instead of parent::setUp($modules).