code: func MethodUsageText(method string) (string, error) {
  	// Look up details about the provided method and error out if not
  	// registered.
  	registerLock.RLock()
  	rtp, ok := methodToConcreteType[method]
  	info := methodToInfo[method]
  	registerLock.RUnlock()
  	if !ok {
  		str := fmt.Sprintf("%q is not registered", method)
  		return "", makeError(ErrUnregisteredMethod, str)
  	}
  
  	// When the usage for this method has already been generated, simply
  	// return it.
  	if info.usage != "" {
  		return info.usage, nil
  	}
  
  	// Generate and store the usage string for future calls and return it.
  	usage := methodUsageText(rtp, info.defaults, method)
  	registerLock.Lock()
  	info.usage = usage
  	methodToInfo[method] = info
  	registerLock.Unlock()
  	return usage, nil
  }
docs: // MethodUsageText returns a one-line usage string for the provided method.  The
  // provided method must be associated with a registered type.  All commands
  // provided by this package are registered by default.