required
| 51 | bool empty() const { return str.empty(); } // required |
| 52 | auto begin() const { return str.begin(); } // required |
| 53 | auto end() const { return str.end(); } // required |
| 54 | void append(std::size_t count, char c) { str.append(count, c); } // required |
| 55 | void append(const char* s, std::size_t size) { str.append(s, size); } // required |
| 56 |