code: func (f Frame) MarshalText() ([]byte, error) {
  	name := f.name()
  	if name == "unknown" {
  		return []byte(name), nil
  	}
  	return []byte(fmt.Sprintf("%s %s:%d", name, f.file(), f.line())), nil
  }
docs: // MarshalText formats a stacktrace Frame as a text string. The output is the
  // same as that of fmt.Sprintf("%+v", f), but without newlines or tabs.