postcss/postcss

The package is an embeddable CSS-processing library distributed through CommonJS and ESM entrypoints with TypeScript declarations. Its runtime separates input handling, tokenization, parsing, plugin orchestration, AST mutation, and serialization. Processing state lives in memory; source-map discovery introduces a filesystem-read boundary, while runners own output persistence. Package scripts and GitHub Actions define validation and publishing rather than an application server deployment.

• package.json routes require to lib/postcss.js, import to lib/postcss.mjs, and typings to lib/postcss.d.ts; the ESM module re-exports the CommonJS API.
  package.json#L37-50lib/postcss.mjs#L1-30
• postcss(...plugins) accepts either variadic plugins or one array and constructs Processor; the entrypoint also exports parse, stringify, fromJSON, node factories, and AST classes.
  lib/postcss.js#L22-27lib/postcss.js#L72-98
• Processor owns the normalized plugin list and selects NoWorkResult only when plugins, parser, stringifier, and syntax are all absent; other processing uses LazyResult.
  lib/processor.js#L8-12lib/processor.js#L44-59
• The default parser boundary is parse → Input → Parser → tokenizer; Parser constructs a Root and consumes tokens through nextToken rather than materializing a complete token list.
  lib/parse.js#L7-11lib/parser.js#L29-39lib/parser.js#L451-486lib/tokenize.js#L260-269
• Node supplies common metadata and operations, Container supplies children and traversal, Root represents CSS, and Document contains roots; Result holds processor, root, options, messages, CSS, and map.
  lib/node.js#L78-105lib/container.js#L34-53lib/document.js#L7-20lib/result.js#L5-17
• The three runtime dependencies are nanoid, picocolors, and source-map-js; browser mappings disable filesystem/path/URL support, terminal highlighting, and source-map-js, with availability checks in Input and MapGenerator.
  package.json#L38-44package.json#L91-95lib/input.js#L14-15lib/map-generator.js#L9-10
• Existing validation scripts cover ESLint, declaration checks, version consistency, c8 coverage, parser integration, and bundle size; unit tests run through uvu with ts-node transpile-only.
  package.json#L80-89tsconfig.json#L2-11
• Tag pushes trigger cleaned-package npm publishing and changelog-based GitHub releases in separate jobs; tests, docs, and development configs are excluded through .npmignore, and publishing is not gated by a test job inside release.yml.
  .github/workflows/release.yml#L1-28.github/workflows/release.yml#L29-41.npmignore#L1-7