Thanks, very interesting. A bit hard to understand this transcript without context but it really reads like SpiderMonkey and Chakra were actually able to parse

Thanks, very interesting. A bit hard to understand this transcript without context but it really reads like SpiderMonkey and Chakra were actually able to parse this. V8 people didn't like it, the others were like "ok, whatever" and they ended up disallowing it in the spec. I guess it allows simplifications in the parsers by not having a "strict or sloppy, don't know" mode for default parameter values, while not blocking actual use cases.