It's not doing nearly as much work as real browsers do!

After all what is a browser other than something that browses? What other characteristics make it "real"?

A real browser is a browser that aspires to be a web browser that can reasonably be used by a (let's say even fairly technical) user to browse the real web. That means handling handling outright adversarial inputs and my point is this is so central to a real browser, it seems it might be hard to retrofit in later.

I gave one example with the null thing, another one would be the section on how the JS API can break the assumptions made by the DOM parser - it similarly sounds like a bug that's really a bug class and a real browser would need a systemic/architecture fix for.