Twig

Twig is a template engine for PHP with a syntax inspired by Django and Jinja, designed to keep view logic clean, secure, and easy to read for both developers and designers. It compiles templates into optimized plain PHP code, providing fast rendering while sandboxing untrusted templates for security-sensitive applications.

Twig is the default templating engine for Symfony and is widely used across the PHP ecosystem, offering a rich expression syntax, template inheritance, extensible filters/functions, and first-class autoescaping to prevent XSS by default.

What You Get

• A concise, Jinja/Django-inspired template syntax with inheritance, blocks, and macros
• Automatic output escaping (autoescaping) enabled by default to prevent XSS
• A sandbox mode for safely rendering templates from untrusted sources
• An extensible architecture (custom filters, functions, tags, and extensions)
• Compilation to plain PHP for fast repeated rendering rather than runtime interpretation

Common Use Cases

• Rendering views in Symfony applications (Twig is Symfony’s default templating engine)
• Generating HTML emails or PDFs from structured templates in PHP projects
• Letting non-developers (designers, content editors) safely edit page templates
• Rendering user-submitted or CMS-managed templates safely via the sandbox extension
• Building static site generators or code generators on top of a PHP templating layer

Under The Hood

Architecture - Twig parses template source into tokens via Lexer.php, builds an AST with Parser.php/ExpressionParser, and compiles that AST into plain PHP via Compiler.php and the Node/NodeVisitor tree, with the compiled PHP class extending Template.php at runtime and Environment.php acting as the central configuration and extension registry. Tech Stack - Twig is pure PHP (8.1+) with minimal runtime dependencies (Symfony polyfills for mbstring/ctype and deprecation-contracts), and uses PHPStan for static analysis and php-cs-fixer for style enforcement in CI. Code Quality - The tests/ directory contains around a hundred PHP test files covering the lexer, parser, compiler, extensions, sandbox, and loader behavior, run via symfony/phpunit-bridge, and the project maintains a phpstan-baseline.neon to track and reduce static-analysis debt over time. API Design - The Environment/Loader split keeps configuration separate from template resolution, and extension points (custom TwigFilter/TwigFunction/TwigTest registration) let applications extend the language without forking the compiler, though understanding compilation internals (Lexer -> Parser -> Compiler) requires more depth than templates alone for anyone writing custom extensions.