I think you are misunderstanding me. I was just trying to answer "how could you concievably write a web browser engine if you are not Apple/MS/Google/Mozilla".

I think you are misunderstanding me. I was just trying to answer "how could you concievably write a web browser engine if you are not Apple/MS/Google/Mozilla". My answer is: focus first on the happy path. There are a ton of websites that could be rendered with a simpler browser engine - I believe also faster and with less memory. Fall back transparently to an established engine if necessary. This is similar to how a tracing JIT compiler makes assumptions about the types of variables, and if these are violated (because the language is dynamic), falls back to the legacy path, an interpreter. I further think, if you sell it right, you could get people running sites like blogs, documentation, wikis, to opt in to "strict" or "lite" or "document" mode, but that is an orthogonal issue.