docs: public String app() {
      if (d1 < 0) {
        // No stack or detail is present
        return asg.length() > 0 ? asg : null;
      } else if (d1 == 0) {
        // Application portion is empty
        return null;
      } else {
        // Application is present along with stack, detail, or sequence
        return substr(asg, 0, d1);
      }
    }