Pug-lexer is a core component of the Pug (formerly Jade) templating engine, responsible for tokenizing Pug code. It parses a Pug template string and breaks it down into a stream of tokens, representing elements, attributes, text, and control structures. These tokens are then used by the Pug parser to construct an abstract syntax tree (AST). Understanding pug-lexer is critical for debugging Pug templates or creating tools that process or analyze Pug code.