Issue #2861840 by tim.plunkett, lauriii: Preprocess functions are not merged when a module registers a theme hook for a theme-provided template

Issue #2704871 by pepegarciag, Mile23, Manuel Garcia, ieguskiza, snehi, gaurav.pahuja, dimaro, rajeshwari10, gargsuchi, pashupathi nath gajawada, penyaskito, xjm, ZeiP, Wim Leers, alexpott: Replace usages of deprecated method drupal_render()

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

Revert "Issue #2704871 by pepegarciag, ieguskiza, snehi, gaurav.pahuja, rajeshwari10, dimaro, gargsuchi, pashupathi nath gajawada, penyaskito, Manuel Garcia, Mile23: Replace usages of deprecated method drupal render()"

This reverts commit ae3ee317.

Issue #2704871 by pepegarciag, ieguskiza, snehi, gaurav.pahuja, rajeshwari10, dimaro, gargsuchi, pashupathi nath gajawada, penyaskito, Manuel Garcia, Mile23: Replace usages of deprecated method drupal render()

Issue #2572643 by alexpott, attiks, Jelle_S, jhodgdon: Fix Drupal.Commenting.FileComment coding standard

Issue #2388247 by pguillard, snehi, joelpittet, sriharsha.uppuluri: Documentation refers to _theme() function, which has been removed

Issue #2493989 by Antti J. Salminen, lauriii, slashrsm: template_preprocess() and other preprocess functions are called even for theme hooks implemented as functions

Issue #939462 by lauriii, Antti J. Salminen, NROTC_Webmaster, mbrett5062, tim.plunkett, tostinni, rteijeiro, dvessel, cilefen, barraponto, theapi, joelpittet, Xano, tuutti, drzraf, Fabianx, markcarver, xjm, catch, Cottser, sun, jenlampton, effulgentsia, davidhernandez, kscheirer, akalata, andypost, hass, rooby, jhodgdon, fubhy, becw, MXT, mlncn, lemunet, chriscalip, mike stewart, PavanL, kevinquillen, gleroux02: Specific preprocess functions for theme hook suggestions are not invoked

Issue #2350949 by Wim Leers: Add hook_page_attachments(_alter)() and deprecate hook_page_build/alter().

Issue #2246675 by rpayanm, johnstorey, holly.ross.drupal | mgbellaire: Remove all unnecessary 'template' lines in hook_theme() declarations.

Issue #2226207 by lauriii, mgbellaire, Cottser, m1r1k, Mark Carver, LinL, rachel_norfolk, rteijeiro, skwashd, davidhernandez, euphoric_mv: Make 'template' the default output option for hook_theme().

Issue #2329795 by fietserwin, bzitzow, alexrayu, tstoeckler | illutek, dawehner: Fixed Make it possible to add information to theme info files during development.

This reverts commit ae8be3cc.

Issue #2173655 by Cottser, xjm, jessebeach, alexpott, rlmumford: Refactor theme() to _theme(); make it a private API to discourage module developers from circumventing the renderable build system.

Issue #2068471 by dawehner, Crell, tim.plunkett, jibran, fubhy, larowlan: Normalize Controller/View-listener behavior with a Page object.

Issue #1954892 by dawehner, David_Rothstein, tim.plunkett: Replace 'theme callback' and hook_custom_theme() with a clean theme negotiation system.

Revert "Issue #1954892 by dawehner, tim.plunkett, David_Rothstein, effulgentsia: Replace 'theme callback' and hook_custom_theme() with a clean theme negotiation system."

This reverts commit fc04601c.

Issue #1954892 by dawehner, tim.plunkett, David_Rothstein, effulgentsia: Replace 'theme callback' and hook_custom_theme() with a clean theme negotiation system.

Issue #1886448 by dawehner, sun, Berdir, ParisLiakos: Rewrite the theme registry into a proper service.

Issue #2049207 by dlu, blakehall, janstoeckler, ramlev, Moderate | Cottser: Replace .tpl.php with .html.twig in documentation.

Issue #1751194 by Cottser, mikl, effulgentsia, benjifisher: Introduce hook_theme_suggestions_HOOK() and hook_theme_suggestions_HOOK_alter().

Issue #1981368 by tim.plunkett, Crell, webchick: Convert all routes to 'module_name().foo_bar()' naming convention.

Issue #2004286 by joelpittet, jenlampton, Cottser, LinL: Defer calls to drupal_get_()* functions until printed inside a template by adding a RenderWrapper class.

Issue #2030457 by Mark Carver, Cottser: Fixed Warning: Missing argument 3 for template_preprocess() for theme functions overridden by templates.

Issue #1972514 by Wim Leers, effulgentsia, Gábor Hojtsy, ekl1773: Fixed Impossible to set attributes for all entities.

Issue #1806478 by Cottser, joelpittet, kevinquillen: Make twig the default engine once all modules templates are converted from .tpl.php to .html.twig.

Issue #1920886 by Cottser, Fabianx: Drupal_render() should only render the child elements when rendering a 'render element' for the first time.

Issue #575298 by sun, tim.plunkett, Rob Loach, KrisBulman, Jacine, danillonunes: Provide non-PHP way to reliably override CSS.

Issue #1168246 by sun, mgifford, Manuel Garcia, mbrett5062, ry5n, Everett Zufelt, nod_, aspilicious, deviantintegral, tim.plunkett: Freedom For Fieldsets! Long Live The DETAILS.