PEG.js – Parser Generator for JavaScript. I stumbled upon it while looking for some parser implementations, including PEG-based parser generators, as I have a PEG definition for Markdown. But I probably need to study some theory before I can use it meaningfully. Or I'll just handcraft the parser - the Markdown syntax isn't really that complicated after all. And for my game project, I need to extend the parser with various custom features anyway.