/a{2,0/; YARR: accepts it OLD: rejects it, saying "maximum {2,0 less than minimum" Both seem engines treat the "{" as literal given the lack of "}", which surprises me. But I guess OLD is being cranky by applying the min<=max rule anyway.

YARR seems to assume that the absence of } means the other characters should be treated as literal characters...

Neither Yarr nor irregexp reject /a{2,0/. ES2015 B.1.4 also seems to allow this syntax -> Resolving as Won't Fix.