MixedHTML Mode for Emacs

Developer jefftk has released mixed-html-mode, a new major mode for the Emacs text editor, created with significant assistance from Anthropic's Claude Code. The tool addresses a specific pain point for web developers: cleanly highlighting syntax in files that mix HTML, inline CSS, and JavaScript. Its core innovation is adopting the browser's simple parsing logic—scanning for literal `<script>` and `<style>` tags—to avoid the confusion and performance issues that plague other modes. jefftk directed Claude through an iterative, hour-long development and debugging session to achieve a reliable tool that is "mildly faster than web-mode" and "far faster than html-ts-mode."

The development process highlights the shifting landscape of software creation. jefftk, who chose Emacs decades ago for its extensibility but rarely used it due to the effort required, found that with an AI assistant, "now it's not much work!" He validated the code through a mix of having Claude review itself, write tests, and personal use, though he admits he hasn't read the code in detail and expects some bugs remain. The primary current limitation is the lack of automatic indentation. This project exemplifies how AI coding agents like Claude are lowering the barrier to creating sophisticated, personalized developer tools, potentially revitalizing older platforms like Emacs by making deep customization accessible.