Issue #3377570 by catch, Wim Leers, mglaman, marcelovani, Kingdutch: Add PHP Fibers support to BigPipe

Issue #2632750 by Wim Leers, bnjmnm, krlucas, ronaldtebrake, zaporylie, mherchel, Fabianx, webchick, yogeshchaugule8, catch, darol100, yoroy, Bojhan, Gábor Hojtsy: Interface previews/skeleton screens through optional "preview" or "placeholder" templates

Issue #3209617 by longwave, daffie, catch: [Symfony 6] Symfony\Component\HttpFoundation\RequestStack::getMasterRequest() is deprecated, use getMainRequest() instead

Issue #2851394 by GoZ, hgunicamp, oknate, jungle, wolffereast, tameeshb, mmatsoo, ridhimaabrol24, jofitz, swarad07, tanc, shaktik, dimaro, shashikant_chauhan, MerryHamster, quietone, nitesh624, martin_q, boaloysius, gaurav.kapoor, nitvirus, ankithashetty, Munavijayalakshmi, kostyashupenko, leolando.tan, amit.drupal, ravi.shankar, akashkrishnan01, Swapnil_Kotwal, Saviktor, mrinalini9, anmolgoyal74, Venkatesh Rajan.J, shimpy, lomasr, Dinesh18, shubham.prakash, mahtab_alam, markdorison, cilefen, longwave, bleen, xjm, alexpott, gmaltoni: Fix grammar 'a' to 'an' when necessary

Issue #3104307 by Berdir, longwave, Gábor Hojtsy, Wim Leers, alexpott, andypost: Remove  BC layers in various Drupal\Core components

Issue #2966327 by alexpott, mcdruid, dww, dsnopek, catch, pwolanin, larowlan, tim.plunkett, Berdir, Sam152: Limit what can be called by a callback in render arrays to reduce the risk of RCE

Issue #2572613 by Malevi4, idebr, pfrenssen, Mile23, RajeevK: Fix 'Drupal.Array.Array.CommaLastItem' coding standard

Issue #2935256 by Jo Fitzgerald, voleger, kim.pepper, ibustos, Yogesh Pawar, catch, jibran: Remove all usages of drupal_get_message and drupal_set_message in modules

Issue #2863607 by Lendude, naveenvalecha, Wim Leers, Jo Fitzgerald: Convert WebTestBaseTests of BigPipe to BrowserTestBase

Issue #2657684 by Wim Leers, Fabianx, xjm, effulgentsia: Refactor BigPipe internals to allow a contrib module to extend BigPipe with the ability to stream anonymous responses and prime Page Cache for subsequent visits

Issue #2567715 by marthinal, hgoto, jpd4nt, mr.baileys, Wim Leers, alexpott: #markup generated by #pre_render callbacks do not get processed by ensureMarkupIsSafe()

Issue #2698811 by danmuzyka, Wim Leers, jhedstrom, Fabianx: BigPipe unnecessarily renders and sends multiple-occurrence placeholders multiple times when using JS — can cause JS errors

Issue #2678568 by Wim Leers: Ensure good UX & DX even when A) rendering of placeholder fails, B) some response event subscriber fails

Revert "Issue #2678568 by Wim Leers: Ensure good UX & DX even when A) rendering of placeholder fails, B) some response event subscriber fails"

This reverts commit eee35007.

Issue #2678568 by Wim Leers: Ensure good UX & DX even when A) rendering of placeholder fails, B) some response event subscriber fails

Issue #2469431 by Wim Leers, Fabianx, swentel, nod_, yched, dawehner, tstoeckler, catch, borisson_: BigPipe for auth users: first send+render the cheap parts of the page, then the expensive parts