htmlnano is a modular HTML minifier built on PostHTML, providing a library API, CLI, PostHTML plugin, and webpack integration. It processes HTML through a configurable pipeline of modules (e.g., whitespace collapse, comment removal, CSS/JS/SVG minification) organized into presets (safe, ampSafe, max). The core architecture uses PostHTML's tree walking and a plugin-like module interface where each module can transform attributes, content, or nodes. Optional peer dependencies (cssnano, terser, svgo, etc.) are loaded lazily, and configuration is handled via cosmiconfig. The codebase demonstrates strong engineering with comprehensive test coverage, property-based fuzz testing, and DOM equivalence validation. While primarily a library, it also includes a CLI and webpack adapter, making it a versatile tool for HTML optimization in build pipelines.