I've known a few people (including myself) who have casually thought about what it would take to write a new browser engine. Obviously it's a titanic undertaking and unrealistic project but one thing I considered recently:
There are a ton of new API's the browser has added since HTML5 giving all sorts of capabilities. Hell, Chrome can access USB devices on your host if you allow it permissions.
But is there a canonical list of all standardized web API's somewhere? Something that a browser engine developer could look at to decide what API's are must haves and what are optional.
> is there a canonical list of all standardized web API's somewhere
MDN[0] is probably the best list intended for this purpose, but it's easier to use if you already know what you're looking for.
While not explicitly its intent, I think caniuse[1] may be a better list for top-level browsing.