The Spec for RegExp V flag reserves character pairs and certain syntax characters as not allowed in the ClassSetCharacter production. Tests are needed to check for these syntax rules as both set operands and class string disjunctions (\q{...}). ClassSetCharacter :: [lookahead ∉ ClassSetReservedDoublePunctuator] SourceCharacter but not ClassSetSyntaxCharacter ... ClassSetReservedDoublePunctuator :: one of && !! ## $$ %% ** ++ ,, .. :: ;; << == >> ?? @@ ^^ `` ~~ ClassSetSyntaxCharacter :: one of ( ) [ ] { } / - \ |