Comparing the Syntax Errors from JSTests/stress/regexp-vflag-property-of-strings.js against what V8/Chrome produce some slightly different results. For example, /[a--;;]/v produces the equivalent of JSC"s "invalid operation in class set" Syntax error instead of an "invalid class set character". Most of the difference are of that type, or a few that are the inverse where V8 produces the equivalent of JSC's "invalid class set character" instead of "invalid operation in class set".