> Given the state of modern HTML5 and CSS standards, and ignoring compatibility and real-world usage (just like for toy compilers), Let's Build A Browser Engine

> Given the state of modern HTML5 and CSS standards, and ignoring compatibility and real-world usage (just like for toy compilers), Let's Build A Browser Engine sounds more tempting than Let's Build a Compiler. FWIW, current HTML and CSS standards should give you compatibility with real-world usage if you implement them accurately. Of course, for a toy, you may well want to simplify things from what the standard does.