docs: public String mkString(String start, String sep, String end) {
  		StringBuilder ret = new StringBuilder(start);
  		for (int i = 0; i < inner.size(); i++) {
  			ret.append(inner.get(i));
  			if (i != (inner.size() - 1)) {
  				ret.append(sep);
  			}
  		}
  		return ret.append(end).toString();
  	}