code: func FprintStackTrace(w io.Writer, err error) {
  	if err, ok := err.(stackTracer); ok {
  		for _, f := range err.StackTrace() {
  			fmt.Fprintf(w, "%+s:%d\n", f, f)
  		}
  	}
  }
docs: // FprintStackTrace prints the error's stack trace to w.