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Code reference map

Code Reference Map

Core Template Engine

File Purpose
core/lib/Drupal/Core/Template/TwigExtension.php All Drupal Twig functions and filters
core/lib/Drupal/Core/Template/TwigEnvironment.php Twig environment setup, sandbox configuration
core/lib/Drupal/Core/Template/Attribute.php Attribute class — addClass(), setAttribute(), etc.
core/lib/Drupal/Core/Template/TwigSandboxPolicy.php Allowed methods/prefixes/classes in sandbox
core/lib/Drupal/Core/Template/DebugExtension.php Debug functions and template path comments
core/lib/Drupal/Core/Template/TwigNodeTrans.php {% trans %} tag implementation
core/lib/Drupal/Core/Template/ComponentsTwigExtension.php SDC Twig functions
core/lib/Drupal/Core/Template/TwigThemeEngine.php Template rendering engine

Theme System

File Purpose
core/lib/Drupal/Core/Theme/ThemeManager.php Template rendering, preprocess calling, default variables
core/lib/Drupal/Core/Theme/Registry.php Theme hook registry, template discovery
core/lib/Drupal/Core/Theme/ThemePreprocess.php OOP implementations: preprocessHtml(), preprocessPage(), preprocessRegion()
core/includes/theme.inc Legacy procedural preprocess functions (deprecated in 11.2)
core/lib/Drupal/Core/Render/theme.api.php hook_theme(), hook_theme_suggestions_HOOK() documentation

Core Templates

Path Templates
core/modules/system/templates/ html.html.twig, page.html.twig, region.html.twig, field.html.twig, block.html.twig
core/modules/node/templates/ node.html.twig and field variants
core/modules/node/src/Hook/NodeThemeHooks.php preprocessNode(), themeSuggestionsNode()
core/modules/views/templates/ views-view.html.twig and display format templates
core/themes/stark/templates/ Minimal reference templates
core/themes/claro/templates/ Modern admin theme patterns

Contrib Modules

Path Purpose
modules/contrib/twig_tweak/src/TwigTweakExtension.php All twig_tweak functions and filters

Drupal API Reference

Topic URL
hook_theme() https://api.drupal.org/api/drupal/core!lib!Drupal!Core!Render!theme.api.php/function/hook_theme/11.x
hook_theme_suggestions_HOOK() https://api.drupal.org/api/drupal/core!lib!Drupal!Core!Render!theme.api.php/function/hook_theme_suggestions_HOOK/11.x
hook_theme_suggestions_HOOK_alter() https://api.drupal.org/api/drupal/core!lib!Drupal!Core!Render!theme.api.php/function/hook_theme_suggestions_HOOK_alter/11.x
Theming Drupal Guide https://www.drupal.org/docs/develop/theming-drupal
Twig in Drupal https://www.drupal.org/docs/theming-drupal/twig-in-drupal
Twig at your Fingertips https://www.drupalatyourfingertips.com/twig