code: func ValidateHostPort(endpoint string, fldPath *field.Path) field.ErrorList {
  	allErrs := field.ErrorList{}
  	if _, _, err := kubeadmutil.ParseHostPort(endpoint); endpoint != "" && err != nil {
  		allErrs = append(allErrs, field.Invalid(fldPath, endpoint, "endpoint is not valid"))
  	}
  	return allErrs
  }
docs: // ValidateHostPort validates host[:port] endpoints