Method at

include/matchit.h:1193–1196

            // non-const to inform users not to mark Id as const.
            template <typename Pattern>
            constexpr auto at(Pattern &&pattern)
            {
                return and_(pattern, *this);
            }

            // non-const to inform users not to mark Id as const.
            constexpr auto at(Ooo const &) { return OooBinder<Type>{*this}; }