Method cardinality

tutorials/external/catch.hpp:7336–7336

        virtual auto validate() const -> Result { return Result::ok(); }
        virtual auto parse( std::string const& exeName, TokenStream const &tokens) const -> InternalParseResult  = 0;
        virtual auto cardinality() const -> size_t { return 1; }

        auto parse( Args const &args ) const -> InternalParseResult {
            return parse( args.exeName(), TokenStream( args ) );