code: func ValidateDiscoveryTokenAPIServer(apiServer string, fldPath *field.Path) field.ErrorList {
  	allErrs := field.ErrorList{}
  	_, _, err := net.SplitHostPort(apiServer)
  	if err != nil {
  		allErrs = append(allErrs, field.Invalid(fldPath, apiServer, err.Error()))
  	}
  	return allErrs
  }
docs: // ValidateDiscoveryTokenAPIServer validates discovery token for API server