Method isFlag

extlibs/catch/include/catch/catch.hpp:8799–8799

        virtual ~BoundRef() = default;
        virtual auto isContainer() const -> bool { return false; }
        virtual auto isFlag() const -> bool { return false; }
    };
    struct BoundValueRefBase : BoundRef {
        virtual auto setValue( std::string const &arg ) -> ParserResult = 0;