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

Issue #2364157 by mpdonadio, dawehner, martin107, Berdir, pcambra, naveenvalecha, tim.plunkett: Replace most existing _url calls with Url objects

Issue #784626 by Wim Leers, Manuel Garcia, jcisio, joelpittet, Bevan, fcaspani, dcmouyard: Default all JS to the footer, allow asset libraries to force their JS to the header

Issue #2368797 by Wim Leers, dawehner, rteijeiro: Optimize ajaxPageState to keep Drupal 8 sites fast on high-latency networks, prevent CSS/JS aggregation from taking down sites and use HTTP GET for AJAX requests

Issue #2358981 by tadityar, tstoeckler, larowlan, mpdonadio, Devin Carlson: Provide a mechanism for dynamic library declarations

Issue #2378263 by Wim Leers: hook_library_alter() must be manually invoked by users of LibraryDiscovery, and has no test coverage

Issue #2328111 by dawehner, martin107, neclimdul: Replace most instances of the DRUPAL_ROOT constant with the app.root container parameter.

Issue #2183075 by valderama, dinarcon, er.pushpinderrana, amitgoyal, umar-ahmad: Tidy up css.gzip and js.gzip configuration.

Issue #2343661 by larowlan, tim.plunkett | xjm: Rename l() to _l() and url() to _url(), and document replacements.

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

Issue #2307717 by Wim Leers, micbar: Fixed Inform Drupal in *.libraries.yml via a new per-JS file "minified" flag whether a JS file has been minified.

Issue #2307419 by Wim Leers: AssetCollectionOptimizerInterface should allow listing and deleting all aggregates (optimized collection assets).

Issue #2208609 by sun, Jalandhar, damiankloip: Move Json utility class into Drupal\Component\Serialization.

Issue #2093161 by rbayliss, haithem_pro, sandipmkhairnar, InternetDevels, longwave, idflood, Sumeet.Pareek, sidharthap, xeniak, ianthomas_uk: Remove all calls to drupal_json_encode() in favour of \Drupal\Component\Utility\Json::encode().

Issue #2168113 by penyaskito, jessebeach, catch: Add leading underscore and other discouragement to drupal_add_css() and drupal_add_js().

Issue #1786490 by Berdir, amateescu, damiankloip, Wim Leers, dawehner: Add caching to the state system.

Revert "Issue #1786490 by Berdir, amateescu, damiankloip, dawehner: Add caching to the state system."

This reverts commit 8ec847cc.

Issue #2100329 by cosmicdreams: Use \Drupal instead of Drupal to make IDEs and static code analyse tools happy.

Issue #1824848 by spearhead93, catch, mtift: Remove drupal_js_version_string() variable (instead of converting it).

Issue #1798738 by alexpott, mtift, tayzlor, ianmthomasuk, Albert Volkman, heyrocker, cam8001: Move css_js_query_string() to state system.

Issue #2014851 by hlieberman, Wim Leers: Fixed Drupal CSS preprocessing breaks protocol-relative paths.

Issue #1198904 by jox, das-peter: Fixed drupal_load_stylsheet() does not comply with standards when using @import.

Issue #352951 by Wim Leers, mfer, mcjim, larowlan, RobLoach, sdboyer, Owen Barton, JohnAlbin: Make JS & CSS Preprocessing Pluggable.