This is a high-performance CSS selector parser that converts CSS selectors to and from an Abstract Syntax Tree (AST), enabling programmatic manipulation and analysis of selectors. It supports all CSS selector specifications from CSS1 through CSS4, includes comprehensive test coverage, TypeScript support, and features like AST traversal with visitor patterns. The tool is designed for web developers and toolsmiths who need to parse, analyze, transform, or generate CSS selectors programmatically, with an interactive playground for testing and visualization.