code: func logFrameHeader(r *http.Request) {
  	framer := os.Getenv("FN_LOGFRAME_NAME")
  	if framer == "" {
  		return
  	}
  	valueSrc := os.Getenv("FN_LOGFRAME_HDR")
  	if valueSrc == "" {
  		return
  	}
  	id := r.Header.Get(valueSrc)
  	if id != "" {
  		fmt.Fprintf(os.Stderr, "\n%s=%s\n", framer, id)
  		fmt.Fprintf(os.Stdout, "\n%s=%s\n", framer, id)
  	}
  }
docs: // If enabled, print the log framing content.